Implement Struct#to_h .

use Kernel#__send__ insteard of Kernel#send

Space

Add doubling stack extend, as fix for #2016

Print file name and line number in codedump if available.

fix disabled stdio

define `resize_capa` as a function

remove `mrb_str_offset`

remove `DBL_DIG` fallback definition

Fix MSVC warning for symbol.c

This increases readability and maintainability,
and it also doesn't use reserved identifiers.

Fix multiline comments

Speed up Array#select! from O(n^2) to O(n).