feat(CI): add a GitHub Action to lint the Markdown

Run on pull request only
Using https://www.npmjs.com/package/markdownlint-cli
Lint Markdown for rules:
- MD009/no-trailing-spaces
- MD012/no-multiple-blanks
- MD022/blanks-around-headings
- MD031/blanks-around-fences
- MD032/blanks-around-lists

12 files changed, 144 insertions, 41 deletions

diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index e04d0fc75..ed1682b05 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -10,3 +10,14 @@ jobs:
       - uses: actions/checkout@v2
       - name: 🧹 YAML Lint
         uses: ibiqlik/action-yamllint@v3
+  markdownlint:
+    name: 🍸 Markdown
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: 🚀 Use Node.js
+        uses: actions/[email protected]
+        with:
+          node-version: '12.x'
+      - run: npm install -g [email protected]
+      - run: markdownlint '**/*.md'
diff --git a/.markdownlint.yml b/.markdownlint.yml
new file mode 100644
index 000000000..b59c6cb53
--- /dev/null
+++ b/.markdownlint.yml
@@ -0,0 +1,16 @@
+MD001: false
+MD003: false
+MD004: false
+MD005: false
+MD007: false
+MD010: false
+MD011: false
+MD013: false
+MD014: false
+MD024: false
+MD025: false
+MD026: false
+MD034: false
+MD040: false
+MD041: false
+MD046: false
diff --git a/doc/guides/compile.md b/doc/guides/compile.md
index b0dedfc8e..527868704 100644
--- a/doc/guides/compile.md
+++ b/doc/guides/compile.md
@@ -6,6 +6,7 @@ binaries.
 ## Prerequisites
 
 To compile mruby out of the source code you need the following tools:
+
 * C Compiler (e.g. `gcc` or `clang`)
 * Linker (e.g. `gcc` or `clang`)
 * Archive utility (e.g. `ar`)
@@ -18,6 +19,7 @@ the `$PATH` to compile `mruby`. We also encourage to upgrade `ruby`
 on MacOS in similar manner.
 
 Optional:
+
 * git (to update mruby source and integrate mrbgems easier)
 * C++ compiler (to use GEMs which include \*.cpp, \*.cxx, \*.cc)
 * Assembler (to use GEMs which include \*.asm)
@@ -61,6 +63,7 @@ configure the build environment for specific compiler infrastructures.
 #### GCC
 
 Toolchain configuration for the GNU C Compiler.
+
 ```ruby
 toolchain :gcc
 ```
@@ -69,6 +72,7 @@ toolchain :gcc
 
 Toolchain configuration for the LLVM C Compiler clang. Mainly equal to the
 GCC toolchain.
+
 ```ruby
 toolchain :clang
 ```
@@ -78,6 +82,7 @@ toolchain :clang
 Toolchain configuration for Visual Studio on Windows. If you use the
 [Visual Studio Command Prompt](https://msdn.microsoft.com/en-us/library/ms229859\(v=vs.110\).aspx),
 you normally do not have to specify this manually, since it gets automatically detected by our build process.
+
 ```ruby
 toolchain :visualcpp
 ```
@@ -85,6 +90,7 @@ toolchain :visualcpp
 #### Android
 
 Toolchain configuration for Android.
+
 ```ruby
 toolchain :android
 ```
@@ -95,7 +101,7 @@ in `ANDROID_STANDALONE_TOOLCHAIN`.
 ### Binaries
 
 It is possible to select which tools should be compiled during the compilation
-process. For example, 
+process. For example,
 
 * `mruby`
 * `mirb`
@@ -106,6 +112,7 @@ The configuration are done via `mrbgems`. See `Mrbgems` section.
 
 Some environments require a different file separator character. It is possible to
 set the character via `conf.file_separator`.
+
 ```ruby
 conf.file_separator = '/'
 ```
@@ -113,6 +120,7 @@ conf.file_separator = '/'
 ### C Compiler
 
 Configuration of the C compiler binary, flags and include paths.
+
 ```ruby
 conf.cc do |cc|
   cc.command = ...
@@ -128,6 +136,7 @@ end
 C Compiler has header searcher to detect installed library.
 
 If you need a include path of header file use `search_header_path`:
+
 ```ruby
 # Searches ```iconv.h```.
 # If found it will return include path of the header file.
@@ -136,6 +145,7 @@ fail 'iconv.h not found' unless conf.cc.search_header_path 'iconv.h'
 ```
 
 If you need a full file name of header file use `search_header`:
+
 ```ruby
 # Searches ```iconv.h```.
 # If found it will return full path of the header file.
@@ -149,6 +159,7 @@ When you are using GCC toolchain (including clang toolchain since its base is gc
 it will use compiler specific include paths too. (For example `/usr/local/include`, `/usr/include`)
 
 If you need a special header search paths define a singleton method `header_search_paths` to C compiler:
+
 ```ruby
 def conf.cc.header_search_paths
   ['/opt/local/include'] + include_paths
@@ -158,6 +169,7 @@ end
 ### Linker
 
 Configuration of the Linker binary, flags and library paths.
+
 ```ruby
 conf.linker do |linker|
   linker.command = ...
@@ -175,6 +187,7 @@ end
 ### Archiver
 
 Configuration of the Archiver binary and flags.
+
 ```ruby
 conf.archiver do |archiver|
   archiver.command = ...
@@ -185,6 +198,7 @@ end
 ### Parser Generator
 
 Configuration of the Parser Generator binary and flags.
+
 ```ruby
 conf.yacc do |yacc|
   yacc.command = ...
@@ -195,6 +209,7 @@ end
 ### GPerf
 
 Configuration of the GPerf binary and flags.
+
 ```ruby
 conf.gperf do |gperf|
   gperf.command = ...
@@ -203,6 +218,7 @@ end
 ```
 
 ### File Extensions
+
 ```ruby
 conf.exts do |exts|
   exts.object = ...
@@ -247,6 +263,7 @@ See doc/mrbgems/README.md for more option about mrbgems.
 Configuration Mrbtest build process.
 
 If you want mrbtest.a only, You should set `conf.build_mrbtest_lib_only`
+
 ```ruby
 conf.build_mrbtest_lib_only
 ```
@@ -259,6 +276,7 @@ See `mruby-bin-*/bintest/*.rb` if you need examples.
 If you want a temporary files use `tempfile` module of CRuby instead of `/tmp/`.
 
 You can enable it with following:
+
 ```ruby
 conf.enable_bintest
 ```
@@ -277,6 +295,7 @@ files are compiled by C++ compiler.
 
 When you mix C++ code, C++ exception would be enabled automatically.
 If you need to enable C++ exception explicitly add the following:
+
 ```ruby
 conf.enable_cxx_exception
 ```
@@ -286,20 +305,24 @@ conf.enable_cxx_exception
 If your compiler does not support C++ and you want to ensure
 you don't use mrbgem written in C++, you can explicitly disable
 C++ exception, add following:
+
 ```ruby
 conf.disable_cxx_exception
 ```
+
 and you will get an error when you try to use C++ gem.
 Note that it must be called before `enable_cxx_exception` or `gem` method.
 
 ### Debugging mode
 
 To enable debugging mode add the following:
+
 ```ruby
 conf.enable_debug
 ```
 
 When debugging mode is enabled
+
 * Macro `MRB_DEBUG` would be defined.
 	* Which means `mrb_assert()` macro is enabled.
 * Debug information of irep would be generated by `mrbc`.
@@ -330,6 +353,7 @@ directory.
 
 In cross compilation, you can run `mrbtest` on emulator if
 you have it by changing configuration of test runner.
+
 ```ruby
 conf.test_runner do |t|
   t.command = ... # set emulator. this value must be non nil or false
@@ -369,6 +393,7 @@ root directory. The structure of this directory will look like this:
 	          +- mruby
 
 The compilation workflow will look like this:
+
 * compile all files under *src* (object files will be stored
 in *build/host/src*)
 * generate parser grammar out of *src/parse.y* (generated
@@ -446,6 +471,7 @@ build directory.
 The cross compilation workflow starts in the same way as the normal
 compilation by compiling all *native* libraries and binaries.
 Afterwards the cross compilation process proceeds like this:
+
 * cross-compile all files under *src* (object files will be stored
 in *build/i386/src*)
 * generate parser grammar out of *src/parse.y* (generated
diff --git a/doc/guides/debugger.md b/doc/guides/debugger.md
index 61c0418b0..9d0c005c4 100644
--- a/doc/guides/debugger.md
+++ b/doc/guides/debugger.md
@@ -220,6 +220,7 @@ Example:
 ```
 
 Enabling all breakpoints
+
 ```
 (foo.rb:1) enable 1 3
 ```
diff --git a/doc/guides/mrbconf.md b/doc/guides/mrbconf.md
index d01eff258..2130d51c2 100644
--- a/doc/guides/mrbconf.md
+++ b/doc/guides/mrbconf.md
@@ -1,7 +1,9 @@
 # mruby configuration macros.
 
 ## How to use these macros.
+
 You can use mrbconfs with following ways:
+
 * Write them in `mrbconf.h`.
  * Using compiler flags is preferred  when building a cross binaries or multiple mruby binaries
  since it's easier to use different mrbconf per each `MRuby::Build`.
@@ -11,7 +13,9 @@ You can use mrbconfs with following ways:
  changes `struct` layout and cause memory access error when C and other language(e.g., C++) is mixed.
 
 ## stdio setting.
+
 `MRB_NO_STDIO`
+
 * When defined `<stdio.h>` functions won't be used.
 * Some features will be disabled when this is enabled:
   * `mrb_irep` load/dump from/to file.
@@ -19,80 +23,97 @@ You can use mrbconfs with following ways:
   * Printing features in **src/print.c**.
 
 ## Debug macros.
+
 `MRB_USE_DEBUG_HOOK`
+
 * When defined code fetch hook and debug OP hook will be enabled.
 * When using any of the hook set function pointer `code_fetch_hook` and/or `debug_op_hook` of `mrb_state`.
 * Fetch hook will be called before any OP.
 * Debug OP hook will be called when dispatching `OP_DEBUG`.
 
 `MRB_DEBUG`
+
 * When defined `mrb_assert*` macro will be defined with macros from `<assert.h>`.
 * Could be enabled via `enable_debug` method of `MRuby::Build`.
 
 ## Stack configuration
 
 `MRB_STACK_EXTEND_DOUBLING`
+
 * If defined doubles the stack size when extending it.
 * Else extends stack with `MRB_STACK_GROWTH`.
 
 `MRB_STACK_GROWTH`
+
 * Default value is `128`.
 * Used in stack extending.
 * Ignored when `MRB_STACK_EXTEND_DOUBLING` is defined.
 
 `MRB_STACK_MAX`
+
 * Default value is `0x40000 - MRB_STACK_GROWTH`.
 * Raises `RuntimeError` when stack size exceeds this value.
 
 ## Primitive type configuration.
 
 `MRB_USE_FLOAT32`
+
 * When defined single precision floating point type(C type `float`) is used as `mrb_float`.
 * Otherwise double precision floating point type(C type `double`) is used as `mrb_float`.
 
 `MRB_NO_FLOAT`
+
 * When defined removes floating point numbers from mruby.
 * It makes mruby easier to handle in "Microcontroller without FPU" and "Kernel Space".
 
 `MRB_INT32`
+
 * When defined, or `MRB_INT64` are not defined on 32-bit CPU mode, `mrb_int` will be defined as `int32_t`.
 * Conflicts with `MRB_INT64`.
 
 `MRB_INT64`
+
 * When defined, or `MRB_INT32` are not defined on 64-bit CPU mode, `mrb_int` will be defined as `int64_t`.
 * Conflicts with `MRB_INT32`.
 
 ## Garbage collector configuration.
 
 `MRB_GC_STRESS`
+
 * When defined full GC is emitted per each `RBasic` allocation.
 * Mainly used in memory manager debugging.
 
 `MRB_GC_TURN_OFF_GENERATIONAL`
+
 * When defined turns generational GC by default.
 
 `MRB_GC_FIXED_ARENA`
+
 * When defined used fixed size GC arena.
 * Raises `RuntimeError` when this is defined and GC arena size exceeds `MRB_GC_ARENA_SIZE`.
 * Useful tracking unnecessary mruby object allocation.
 
 `MRB_GC_ARENA_SIZE`
+
 * Default value is `100`.
 * Ignored when `MRB_GC_FIXED_ARENA` isn't defined.
 * Defines fixed GC arena size.
 
 `MRB_HEAP_PAGE_SIZE`
+
 * Defines value is `1024`.
 * Specifies number of `RBasic` per each heap page.
 
 ## Memory pool configuration.
 
 `POOL_ALIGNMENT`
+
 * Default value is `4`.
 * If you're allocating data types that requires alignment more than default value define the
 largest value of required alignment.
 
 `POOL_PAGE_SIZE`
+
 * Default value is `16000`.
 * Specifies page size of pool page.
 * Smaller the value is increases memory overhead.
@@ -100,32 +121,38 @@ largest value of required alignment.
 ## State atexit configuration.
 
 `MRB_FIXED_STATE_ATEXIT_STACK`
+
 * If defined enables fixed size `mrb_state` atexit stack.
 * Raises `RuntimeError` when `mrb_state_atexit` call count to same `mrb_state` exceeds
 `MRB_FIXED_STATE_ATEXIT_STACK_SIZE`'s value.
 
 `MRB_FIXED_STATE_ATEXIT_STACK_SIZE`
+
 * Default value is `5`.
 * If `MRB_FIXED_STATE_ATEXIT_STACK` isn't defined this macro is ignored.
 
 ## `mrb_value` configuration.
 
 `MRB_ENDIAN_BIG`
+
 * If defined compiles mruby for big endian machines.
 * Used in `MRB_NAN_BOXING`.
 * Some mrbgem use this mrbconf.
 
 `MRB_NAN_BOXING`
+
 * If defined represent `mrb_value` in boxed `double`.
 * Conflicts with `MRB_USE_FLOAT32` and `MRB_NO_FLOAT`.
 
 `MRB_WORD_BOXING`
+
 * If defined represent `mrb_value` as a word.
 * If defined `Float` will be a mruby object with `RBasic`.
 
 ## Reduce heap memory configuration.
 
 `MRB_USE_LINK_TIME_RO_DATA_P`
+
 * Only available on ELF platforms.
 * If you specify the address of a read-only section when creating a symbol or string, that string will be used as it is.
 * Heap memory can be saved.
@@ -133,6 +160,7 @@ largest value of required alignment.
 * It must be `__ehdr_start < data_addr < __init_array_start`.
 
 `MRB_USE_CUSTOM_RO_DATA_P`
+
 * Takes precedence over `MRB_USE_LINK_TIME_RO_DATA_P`.
 * Please try if `MRB_USE_LINK_TIME_RO_DATA_P` is not available.
 * The `mrb_ro_data_p()` function is implemented by the user in an arbitrary file.
@@ -140,33 +168,41 @@ largest value of required alignment.
 * Return `TRUE` if `ptr` is in read-only section, otherwise return `FALSE`.
 
 ## Other configuration.
+
 `MRB_UTF8_STRING`
+
 * Adds UTF-8 encoding support to character-oriented String instance methods.
 * If it isn't defined, they only support the US-ASCII encoding.
 
 `MRB_FUNCALL_ARGC_MAX`
+
 * Default value is `16`.
 * Specifies 4th argument(`argc`) max value of `mrb_funcall`.
 * Raises `ArgumentError` when the `argc` argument is bigger then this value `mrb_funcall`.
 
 `KHASH_DEFAULT_SIZE`
+
 * Default value is `32`.
 * Specifies default size of khash table bucket.
 * Used in `kh_init_ ## name` function.
 
 `MRB_NO_METHOD_CACHE`
+
 * Disable method cache to save memory.
 
 `MRB_METHOD_CACHE_SIZE`
+
 * Default value is `256`.
 * Ignored if `MRB_NO_METHOD_CACHE` is defined.
 * Need to be the power of 2.
 
 `MRB_USE_METHOD_T_STRUCT`
+
 * Use C struct to represent `mrb_method_t`
 * No `MRB_USE_METHOD_T_STRUCT` requires highest 2 bits of function pointers to be zero
 * Define this macro on machines that use higher bits of pointers
 
 `MRB_USE_ALL_SYMBOLS`
+
 * Make it available `Symbol.all_symbols` in `mrbgems/mruby-symbol-ext`
 * Increase heap memory usage.
diff --git a/doc/guides/mrbgems.md b/doc/guides/mrbgems.md
index 7120901ee..3dadf4b93 100644
--- a/doc/guides/mrbgems.md
+++ b/doc/guides/mrbgems.md
@@ -18,13 +18,14 @@ You can also use a relative path to specify a gem.
 conf.gem 'examples/mrbgems/ruby_extension_example'
 ```
 
-In that case, 
+In that case,
 
 * if your build configuration file is in the `build_config` directory, it's
   relative from `MRUBY_ROOT`.
 * otherwise, it is relative from the directory where your build configuration is.
 
 A remote GIT repository location for a GEM is also supported:
+
 ```ruby
 conf.gem :git => 'https://github.com/masuidrive/mrbgems-example.git', :branch => 'master'
 conf.gem :github => 'masuidrive/mrbgems-example', :branch => 'master'
@@ -32,17 +33,20 @@ conf.gem :bitbucket => 'mruby/mrbgems-example', :branch => 'master'
 ```
 
 You can specify the sub directory of the repository with `:path` option:
+
 ```ruby
 conf.gem github: 'mruby/mruby', path: 'mrbgems/mruby-socket'
 ```
 
 To use mrbgem from [mgem-list](https://github.com/mruby/mgem-list) use `:mgem` option:
+
 ```ruby
 conf.gem :mgem => 'mruby-yaml'
 conf.gem :mgem => 'yaml' # 'mruby-' prefix could be omitted
 ```
 
 For specifying commit hash to checkout use `:checksum_hash` option:
+
 ```ruby
 conf.gem mgem: 'mruby-redis', checksum_hash: '3446d19fc4a3f9697b5ddbf2a904f301c42f2f4e'
 ```
@@ -66,6 +70,7 @@ via `config.gem`, but wrapped in an `MRuby::GemBox` object.  GemBoxes are
 loaded into mruby via `config.gembox 'boxname'`.
 
 Below we have created a GemBox containing *mruby-time* and *mrbgems-example*:
+
 ```ruby
 MRuby::GemBox.new do |conf|
   conf.gem "#{root}/mrbgems/mruby-time"
@@ -80,14 +85,17 @@ picked up by mruby.
 To use this example GemBox, we save it as `custom.gembox` inside the *mrbgems*
 directory in mruby, and add the following to your build configuration file inside
 the build block:
+
 ```ruby
 conf.gembox 'custom'
 ```
+
 This will cause the *custom* GemBox to be read in during the build process,
 adding *mruby-time* and *mrbgems-example* to the build.
 
 If you want, you can put GemBox outside of mruby directory. In that case you must
 specify an absolute path like below.
+
 ```ruby
 conf.gembox "#{ENV["HOME"]}/mygemboxes/custom"
 ```
@@ -125,6 +133,7 @@ to compile C and Ruby files. *README.md* is a short description of your GEM.
 
 mrbgems expects a specification file called *mrbgem.rake* inside of your
 GEM directory. A typical GEM specification could look like this for example:
+
 ```ruby
 MRuby::Gem::Specification.new('c_and_ruby_extension_example') do |spec|
   spec.license = 'MIT'
@@ -154,6 +163,7 @@ The `license` and `author` properties are required in every GEM!
 
 In case your GEM is depending on other GEMs please use
 `spec.add_dependency(gem, *requirements[, default_get_info])` like:
+
 ```ruby
 MRuby::Gem::Specification.new('c_and_ruby_extension_example') do |spec|
   spec.license = 'MIT'
@@ -177,6 +187,7 @@ end
 The version requirements and default gem information are optional.
 
 Version requirement supports following operators:
+
 * '=': is equal
 * '!=': is not equal
 * '>': is greater
@@ -197,10 +208,12 @@ When a special version of dependency is required,
 use `MRuby::Build#gem` in the build configuration to override default gem.
 
 If you have conflicting GEMs use the following method:
+
 * `spec.add_conflict(gem, *requirements)`
     * The `requirements` argument is same as in `add_dependency` method.
 
 like following code:
+
 ```ruby
 MRuby::Gem::Specification.new 'some-regexp-binding' do |spec|
   spec.license = 'BSD'
@@ -243,7 +256,6 @@ For example: when B depends to C and A depends to B, A will get include paths ex
 Exported include_paths are automatically appended to GEM local include_paths by rake.
 You can use `spec.export_include_paths` accessor if you want more complex build.
 
-
 ## C Extension
 
 mruby can be extended with C. This is possible by using the C API to
@@ -255,6 +267,7 @@ mrbgems expects that you have implemented a C method called
 `mrb_YOURGEMNAME_gem_init(mrb_state)`. `YOURGEMNAME` will be replaced
 by the name of your GEM. If you call your GEM *c_extension_example*, your
 initialisation method could look like this:
+
 ```C
 void
 mrb_c_extension_example_gem_init(mrb_state* mrb) {
@@ -299,7 +312,6 @@ mruby can be extended with pure Ruby. It is possible to override existing
 classes or add new ones in this way. Put all Ruby files into the *mrblib*
 folder.
 
-
 ### Pre-Conditions
 
 none
diff --git a/doc/limitations.md b/doc/limitations.md
index 8ac959b98..f9e81a920 100644
--- a/doc/limitations.md
+++ b/doc/limitations.md
@@ -13,7 +13,6 @@ This document is collecting these limitations.
 This document does not contain a complete list of limitations.
 Please help to improve it by submitting your findings.
 
-
 ## `1/2` gives `0.5`
 
 Since mruby does not have `Bignum`, bigger integers are represented
@@ -72,6 +71,7 @@ rescue => e
   raise e
 end
 ```
+
 ## Fiber execution can't cross C function boundary
 
 mruby's `Fiber` is implemented in a similar way to Lua's co-routine. This
@@ -252,7 +252,7 @@ trace (most recent call last):
 ## Keyword arguments
 
 mruby keyword arguments behave slightly different from CRuby 2.5
-to make the behavior simpler and less confusing. 
+to make the behavior simpler and less confusing.
 
 #### Ruby [ruby 2.5.1p57 (2018-03-29 revision 63029)]
 
@@ -290,6 +290,7 @@ Ruby outputs `falsy`. mruby outputs `truthy`.
 def m(a,(b,c),d); p [a,b,c,d]; end
 m(1,[2,3],4)  # => [1,2,3,4]
 ```
+
 Destructured arguments (`b` and `c` in above example) cannot be accessed
 from the default expression of optional arguments and keyword arguments,
 since actual assignment is done after the evaluation of those default
diff --git a/mrbgems/mruby-io/README.md b/mrbgems/mruby-io/README.md
index 51bdbe014..db52c4a74 100644
--- a/mrbgems/mruby-io/README.md
+++ b/mrbgems/mruby-io/README.md
@@ -4,6 +4,7 @@ mruby-io
 `IO` and `File` classes for mruby
 
 ## Installation
+
 Add the line below to your build configuration.
 
 ```
@@ -13,6 +14,7 @@ Add the line below to your build configuration.
 ## Implemented methods
 
 ### IO
+
  - https://doc.ruby-lang.org/ja/1.9.3/class/IO.html
 
 | method                     | mruby-io | memo |
@@ -97,6 +99,7 @@ Add the line below to your build configuration.
 | IO#write_nonblock          |          |      |
 
 ### File
+
  - https://doc.ruby-lang.org/ja/1.9.3/class/File.html
 
 | method                      | mruby-io | memo |
@@ -167,26 +170,25 @@ Add the line below to your build configuration.
 | File#size                   |          |      |
 | File#truncate               |          |      |
 
-
 ## License
 
 Copyright (c) 2013 Internet Initiative Japan Inc.
 Copyright (c) 2017 mruby developers
 
-Permission is hereby granted, free of charge, to any person obtaining a 
-copy of this software and associated documentation files (the "Software"), 
-to deal in the Software without restriction, including without limitation 
-the rights to use, copy, modify, merge, publish, distribute, sublicense, 
-and/or sell copies of the Software, and to permit persons to whom the 
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
 Software is furnished to do so, subject to the following conditions:
 
-The above copyright notice and this permission notice shall be included in 
+The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
-FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
diff --git a/mrbgems/mruby-pack/README.md b/mrbgems/mruby-pack/README.md
index c66945cde..efa51cc1b 100644
--- a/mrbgems/mruby-pack/README.md
+++ b/mrbgems/mruby-pack/README.md
@@ -3,8 +3,8 @@ mruby-pack (pack / unpack)
 
 mruby-pack provides `Array#pack` and `String#unpack` for mruby.
 
-
 ## Installation
+
 Add the line below into your build configuration:
 
 ```
@@ -13,8 +13,8 @@ Add the line below into your build configuration:
 
 There is no dependency on other mrbgems.
 
-
 ## Supported template string
+
  - A : arbitrary binary string (space padded, count is width)
  - a : arbitrary binary string (null padded, count is width)
  - C : 8-bit unsigned (unsigned char)
@@ -44,28 +44,25 @@ There is no dependency on other mrbgems.
  - x : null byte
  - Z : same as "a", except that null is added with *
 
-
-
 ## License
 
 Copyright (c) 2012 Internet Initiative Japan Inc.
 Copyright (c) 2017 mruby developers
 
-Permission is hereby granted, free of charge, to any person obtaining a 
-copy of this software and associated documentation files (the "Software"), 
-to deal in the Software without restriction, including without limitation 
-the rights to use, copy, modify, merge, publish, distribute, sublicense, 
-and/or sell copies of the Software, and to permit persons to whom the 
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
 Software is furnished to do so, subject to the following conditions:
 
-The above copyright notice and this permission notice shall be included in 
+The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
-FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
-
diff --git a/mrbgems/mruby-sleep/README.md b/mrbgems/mruby-sleep/README.md
index 68aa2c6d3..0ccc7000f 100644
--- a/mrbgems/mruby-sleep/README.md
+++ b/mrbgems/mruby-sleep/README.md
@@ -1,7 +1,9 @@
 # Sleep Module for mruby
+
 mruby sleep module
 
 ## install by mrbgems
+
 - add conf.gem line to your build configuration.
 
 ```ruby
@@ -21,8 +23,7 @@ usleep(10000)
 ```
 
 # License
+
 under the MIT License:
 
 * https://www.opensource.org/licenses/mit-license.php
-
-
diff --git a/mrbgems/mruby-socket/README.md b/mrbgems/mruby-socket/README.md
index 947a24e9e..fd20548aa 100644
--- a/mrbgems/mruby-socket/README.md
+++ b/mrbgems/mruby-socket/README.md
@@ -4,8 +4,8 @@ mruby-socket
 "mruby-socket" mrbgem provides BSD socket interface for mruby.
 API is compatible with CRuby's "socket" library.
 
-
 ## Example
+
 ```sh
 % vi kame.rb
 s = TCPSocket.open("www.kame.net", 80)
@@ -20,18 +20,19 @@ Date: Tue, 21 May 2013 04:31:30 GMT
 ```
 
 ## Requirement
+
 - [mruby-io](https://github.com/mruby/mruby/tree/master/mrbgems/mruby-io) mrbgem
 - [iij/mruby-mtest](https://github.com/iij/mruby-mtest) mrgbem to run tests
 - system must have RFC3493 basic socket interface
 - and some POSIX API...
 
 ## TODO
+
 - add missing methods
 - write more tests
 - fix possible descriptor leakage (see XXX comments)
 - `UNIXSocket#recv_io` `UNIXSocket#send_io`
 
-
 ## License
 
 Copyright (c) 2013 Internet Initiative Japan Inc.
diff --git a/mrbgems/mruby-test/README.md b/mrbgems/mruby-test/README.md
index fa4b91e3a..c0bceecd7 100644
--- a/mrbgems/mruby-test/README.md
+++ b/mrbgems/mruby-test/README.md
@@ -4,4 +4,3 @@ Running Tests
 To run the tests, execute the following from the project's root directory.
 
     $ make test
-