Add support for compiling literate coffeescript

For those of us who like obscure programming techniques from the 90's, this guard has been seriously lacking. This pull request aims to change that.

Changes:
* Add watching of `.coffee.md` and `.litcoffee` [(listed here)](http://ashkenas.com/literate-coffeescript/)
* Automatically detect need to pass `--literate` to the compiler
* Updates tests and docs to reflect changes