Rename MRB_OPSYM() to MRB_QSYM().

Where `QSYM` means quoted symbols, which cannot be represented C
symbols, so specify aliases instead.

- operators: name of the operation, e.g. add for `+`
- predicates: add `_p` suffix instead of `?`
- bang methods: add `_b` suffix instead of `!`
- instance variables: add `a_` prefix instead of `@`
- global variables: add `d_` prefix instead of `@`
- class variables: unsupported; don't use them

src/kernel.c

@@ -766,7 +766,7 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 {
   mrb_value v = mrb_get_arg1(mrb);
   mrb_int i, len;
-  mrb_sym eqq = MRB_OPSYM(eqq);
+  mrb_sym eqq = MRB_QSYM(eqq);
   mrb_value ary;
 
   if (mrb_array_p(self)) {

src/symbol.c

@@ -14,10 +14,10 @@
 
 #undef MRB_PRESYM_MAX
 #undef MRB_PRESYM_CSYM
-#undef MRB_PRESYM_OPSYM
+#undef MRB_PRESYM_QSYM
 #undef MRB_PRESYM_SYM
 #define MRB_PRESYM_CSYM(sym, num) #sym,
-#define MRB_PRESYM_OPSYM(op, sym, num) #op,
+#define MRB_PRESYM_QSYM(sym, name, num) #sym,
 #define MRB_PRESYM_SYM(sym, num) #sym,
 
 static const char *presym_table[] = {