Remove compiler warning

Add the type check in mrb_str_to_cstr().

Extract stack zero filling into new function.

DATA_TYPE must be set as soon as possible

mrb_sys_fail raises an instance of (subclass of) SystemCallError if we have it

Cut off eval_test from main

Add null check

Extract stack zero filling to stack_clear(). Porting evelopers can optimize by replacing to memset() on their own risk.

Remove str_alloc(). Use mrb_obj_alloc_string() instead.

Remove mrb_str_sublen() as it is not used.

Remove mrb_str_new2().

Rename STR_BUF_MIN_SIZE to MRB_STR_BUF_MIN_SIZE. Make it configurable.

Remove unused return value in mruby.c

Use suitable types for variables.

Use suitable types for variables.

Fix indents in parse.y.

Add static declaration

 Make mrb_str_new_cstr() accept NULL pointer. It generates 0byte strings by NULL pointer.

fix inspect method

Fix indent in string.c