Parse mattr_* and cattr_* module accessors, writers and readers

[thenoseman]

Hi!

This very simple change allows the parser to emit tags not only for attr* methods but also their module/class counterparts mattr and cattr_.

Thanks for creating ripper-tags, just found it and fully replaced ctags for my ruby development in vim.

Cheers, Frank

[mislav]

Looks great; thank you!