Move src/re.h to include/mruby/re.h .
Use mruby/re.h instead of duplicate definition.
convert exception message to string

fixes: mruby -e "p ArgumentError.new(1)"
get classname and concatenate ": " only once
various functions should have internal linkage
Merge pull request #2067 from take-cheeze/move_re_h

Move src/re.h to include/mruby/re.h .
Merge pull request #2068 from cremno/exc_inspect-convert-mesg-to-string

convert exception message to string
Merge pull request #2069 from cremno/static

various functions should have internal linkage
raises an ArgumentError when calling #call

based on a patch from @ksss; close #2070
Symbol#to_proc to support block call.

based on a patch from @ksss; close #2071
Add mrb_regexp_p to check whether mrb_value is Regexp.
Use mrb_regexp_p to check regexp.
Merge pull request #2072 from take-cheeze/mrb_regexp_p

Add mrb_regexp_p.
Implement String#index, fixes #2073
Handle utf-8 code in index/rindex
Cosmetic change
Merge pull request #2074 from mattn/fix_string_utf8_index

Implement String#index, fixes #2073
mruby-string-utf8: String#reverse! may leak memory when mrb_str_modify() raises exception
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