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/
Unused block argument - `violations`. If it's necessary, use `_` or `_violations` as an argument name to indicate that it won't be used.