Change name and usage of presym macros

To be also able to build mruby without presym in the future. However,
`MRB_QSYM` has been removed and changed as follows:

### Example

|       Type                | Symbol |  Previous Style  |   New Style    |
|---------------------------|--------|------------------|----------------|
| Operator                  | &      | MRB_QSYM(and)    | MRB_OPSYM(and) |
| Class Variable            | @@foo  | MRB_QSYM(00_foo) | MRB_CVSYM(foo) |
| Instance Variable         | @foo   | MRB_QSYM(0_foo)  | MRB_IVSYM(foo) |
| Method with Bang          | foo!   | MRB_QSYM(foo_b)  | MRB_SYM_B(foo) |
| Method with Question mark | foo?   | MRB_QSYM(foo_p)  | MRB_SYM_Q(foo) |
| Mmethod with Equal        | foo=   | MRB_QSYM(foo_e)  | MRB_SYM_E(foo) |

This change makes it possible to define, for example, `MRB_IVSYM(foo)` as
`mrb_intern_lit(mrb, "@" "foo")`, which is useful if we support building
without presym in the future.

1 files changed, 2 insertions, 6 deletions

diff --git a/src/symbol.c b/src/symbol.c
index add093d14..7a352a477 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -13,12 +13,8 @@
 #include <mruby/class.h>
 
 #undef MRB_PRESYM_MAX
-#undef MRB_PRESYM_CSYM
-#undef MRB_PRESYM_QSYM
-#undef MRB_PRESYM_SYM
-#define MRB_PRESYM_CSYM(sym, num) {#sym,sizeof(#sym)-1},
-#define MRB_PRESYM_QSYM(str, name, num) {str,sizeof(str)-1},
-#define MRB_PRESYM_SYM(str, num) {str,sizeof(str)-1},
+#define MRB_PRESYM_NAMED(lit, num, type, name) {lit, sizeof(lit)-1},
+#define MRB_PRESYM_UNNAMED(lit, num) {lit, sizeof(lit)-1},
 
 static const struct {
   const char *name;