ruby.h: export keyword argument functions

* include/ruby/ruby.h (rb_get_kwargs, rb_extract_keywords): export
  keyword argument functions.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48590 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* remove trailing spaces.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48591 b2dd03c8-39d4-4d8f-98ff-823fe69b080e