add MRB_INT_BIT

add including limits.h.

add mrb_strlen_lit

Because Android's libc(bionic) defines SIZE_MAX at limits.h.

strlen(3) + string literal is usually optimized but strlen(3) doesn't
check if its argument is really a string literal. This is important for
mruby's _static functions to which some _lit macros are expanded (string
literals have static storage). See comment for some additional info.

remove unnecessary parentheses

ignore *.pdb

Added a short description about mruby gems

Suppress warnings.

Fix mrb_funcall calling.

fix sym_intern argument type

add assertion method `assert_nothing_raised'

set bit field for mrb_bool

set bool macro

Reduce mrb_open calls in mrbgem test.

Add comments at end of include guard

Add comments to notify files are auto generated.

Use mrb_str_new_cstr() instead of mrb_str_new() with strlen().

use mrb_str_cat_lit for literals