Add CoffeeScript support

* Use [CoffeeLint] to keep to a community-supported open source standard.
* Memoize the HTTP requests.
* Add flag to enable CoffeeScript
* Rename `Null` style guide to `Unsupported`

[CoffeeLint]: http://www.coffeelint.org/
I don't think this should be decided as part of this pull request. I'm open to discuss this elsewhere, since we are branching to other languages.