Implement String#ord, String#split for mruby-string-utf8
Merge pull request #2075 from mattn/utf8-string-ord

Implement String#ord, String#split for mruby-string-utf8
Add test for String#ord, String#split for mruby-string-utf8
Add one more test
Add a block argument with Array#uniq_bang
Add a block argument with Array#uniq
mruby-string-utf8: str_subseq takes UTF-8 index, not byte index; ref #2076
mruby-string-utf8: update UTF-8 tests; ref #2076
Merge pull request #2078 from suzukaze/add-block-with-array.uniq_bang

Add block argument with Array#uniq! and Array#uniq