Allow class specific arguments so user may open less tabs. Refactor some...

I forgot to fork before pulling so I lost all my commit messages, but basically:
- I tried docpeeker and noticed that running "docpeeker to_s" opened a bunch of nonspecific tabs. I wanted a way to call "docpeeker Array.each"
- I turned RUBYDOC_URLS to a hash and added a few private methods to interpret the reader input if they specify a class name for their method.
- Refactored a bit to still allow the original version to work.

New example usage:
docpeeker map
docpeeker Integer#to_s 
docpeeker Array.slice