use implicit return
use other assert_* methods
use oniguruma api directly
use MRB_SET_INSTANCE_TT instead of instance variable
remove unnecessary struct
remove onig_regexp_init
add OnigRegexp.version
implement native OnigMatchData with OnigRegion
use mrb_intern_lit instead of mrb_intern_cstr
add test for OnigMatchData.new
Merge pull request #9 from take-cheeze/use_oniguruma_api

Refactoring.
last_match isn't set