Add OPTION_NAME_REGEX, a standardized method of parsing option names.

Allows putting example option values in option names to make `brew options formula` as useful as possible.  See [this comment](https://github.com/Homebrew/homebrew/commit/d21ccee108fc56d56f912b10e48969c373356cb9#commitcomment-8843913) for more details.
To be perfectly honest, I couldn't figure out how to expose a constant in ruby.  I thought about defining it in `globals.rb`, similar to the stuff in `tap_constants.rb`, but I liked the idea of making it belong to `Option`.  I tried creating a `@@OPTION_NAME_REGEX`, but I didn't know how to make it accessible to the outside world.  In short, I don't know how Ruby works.  :P

Any tips here would be helpful.