Added support for more styles via citeproc-ruby

Hi!

I added support for a bunch of new styles via citeproc-ruby. I hope you like this pull request.

I would suggest the following things:
* citeproc already contains a chicage style. You might want to consider removing the existing one. Besides, the citeproc's ieee style is also a numeric style
* I hope inukshuk will update his great citeproc-ruby library soon. It seems he's currently working on a new version containing all styles from citationstyles.org!

Cheers,
Michel