feat(CI): add the GitHub Super Linter

The GitHub Super Linter is a more robust and better supported
tool than the current GitHub Actions we are using.

Running these checks:

ERROR_ON_MISSING_EXEC_BIT: true
VALIDATE_BASH: true
VALIDATE_BASH_EXEC: true
VALIDATE_EDITORCONFIG: true
VALIDATE_MARKDOWN: true
VALIDATE_SHELL_SHFMT: true
VALIDATE_YAML: true

https://github.com/marketplace/actions/super-linter
https://github.com/github/super-linter

Added the GitHub Super Linter badge to the README.

Also updated the pre-commit framework and added
more documentation on pre-commit.

Added one more pre-commit check: check-executables-have-shebangs

Added one extra check for merge conflicts to our
GitHub Actions.

EditorConfig and Markdown linting.

Minor grammar and spelling fixes.

Update linter.yml

3 files changed, 4 insertions, 4 deletions

diff --git a/src/fmt_fp.c b/src/fmt_fp.c
index 448c20df8..d3fe97ce3 100644
--- a/src/fmt_fp.c
+++ b/src/fmt_fp.c
@@ -123,7 +123,7 @@ fmt_u(uint32_t x, char *s)
   return s;
 }
 
-/* Do not override this check. The floating point printing code below
+/* Do not override this check. The floating-point printing code below
  * depends on the float.h constants being right. If they are wrong, it
  * may overflow the stack. */
 #if LDBL_MANT_DIG == 53
diff --git a/src/numeric.c b/src/numeric.c
index edb5d28b2..504a7493d 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -232,7 +232,7 @@ coerce_step_counter(mrb_state *mrb, mrb_value self)
  * Document-class: Float
  *
  *  <code>Float</code> objects represent inexact real numbers using
- *  the native architecture's double-precision floating point
+ *  the native architecture's double-precision floating-point
  *  representation.
  */
 
@@ -812,7 +812,7 @@ flo_ceil(mrb_state *mrb, mrb_value num)
  *     flt.round([ndigits])  ->  integer or float
  *
  *  Rounds <i>flt</i> to a given precision in decimal digits (default 0 digits).
- *  Precision may be negative.  Returns a floating point number when ndigits
+ *  Precision may be negative.  Returns a floating-point number when ndigits
  *  is more than zero.
  *
  *     1.4.round      #=> 1
diff --git a/src/string.c b/src/string.c
index eb4136b10..74263098a 100644
--- a/src/string.c
+++ b/src/string.c
@@ -2570,7 +2570,7 @@ mrb_str_to_dbl(mrb_state *mrb, mrb_value str, mrb_bool badcheck)
  *     str.to_f   => float
  *
  *  Returns the result of interpreting leading characters in <i>str</i> as a
- *  floating point number. Extraneous characters past the end of a valid number
+ *  floating-point number. Extraneous characters past the end of a valid number
  *  are ignored. If there is not a valid number at the start of <i>str</i>,
  *  <code>0.0</code> is returned. This method never raises an exception.
  *