reduce mrb_open calls in mrbgem test
add comments at end of include guard
Merge pull request #1839 from cubicdaiya/issues/comment_include_guard

Add comments at end of include guard
Merge pull request #1838 from take-cheeze/reduce_mrb_open_in_test

Reduce mrb_open calls in mrbgem test.
set bit field for mrb_bool
set bool macro
Merge pull request #1841 from ksss/symbol-bool

set bool macro
Merge pull request #1840 from ksss/bit-field

set bit field for mrb_bool
add assertion method `assert_nothing_raised'
Merge pull request #1842 from ksss/assert_nothing_raised

add assertion method `assert_nothing_raised'