Enumerable#minmax_by
Suppoert multiple values in Enumerable#minmax_by
Merge pull request #1920 from suzukaze/add-enum.minmax_by

Add Enumerable#minmax_by
Use MRB_ARGS_REST() instead of ARGS_REST()

According to include/mruby.h,

 /* compatibility macros; will be removed */
 #define ARGS_REST()         MRB_ARGS_REST()
Add Enumerable#none?
Support multiple values in Enumerable#none?
Hash#{select,select!} support return Enumerator
if non block given
Hash#{select,select!} fix yield value
Merge pull request #1922 from suzukaze/add-enum.none

Add Enumerable.none?
Merge pull request #1923 from ksss/hash-enumerator-select

Hash#{select,select!} support return Enumerator
Merge pull request #1921 from cubicdaiya/issues/not_use_old_macro

Use MRB_ARGS_REST() instead of ARGS_REST()
mrb_str_pool use embed-string
Hash#{reject,reject!} support return Enumerator
Hash#{reject,reject!} fix yield value
Merge pull request #1925 from ksss/hash-reject

Hash#{reject,reject!} support return Enumerator
Add Enumerable#one?
Merge pull request #1926 from suzukaze/add-enum.one

Add Enumerable#one?
Enumerable#one? to prune iteration when count > 1; ref #1926
move conditional out of loop