Add Array#delete_if
Use boolean macro in is_valid_c_symbol_name()
use `stack_type` instead of raw `unsigned int`
allow method definition in cmdarg

save cmdarg_stack and isolate command argument state from outer scope
to allow method definition in cmdarg

import from ruby/ruby@04bb9d6b75a55d4000700769eead5a5cb942c25b
Merge pull request #2094 from suzukaze/add-array.delete_if

Add Array#delete_if
Merge pull request #2095 from suzukaze/refactor-dump.c

Use boolean macro in is_valid_c_symbol_name()
Merge pull request #2096 from nobu/def_in_cmdarg

Def in cmdarg