Literate CoffeeScript should be rendered as Markdown

From [the CoffeeScript website](http://coffeescript.org/#literate):

> Besides being used as an ordinary programming language, CoffeeScript may also be written in "literate" mode. If you name your file with a  .litcoffee extension, you can write it as a Markdown document — a document that also happens to be executable CoffeeScript code. The compiler will treat any indented blocks (Markdown's way of indicating source code) as code, and ignore the rest as comments.

A good example of literate CoffeeScript is [the file used to test it from CoffeeScript’s test suite](https://github.com/jashkenas/coffee-script/blob/master/test/literate.litcoffee).

For the purposes of this project, this effectively means that `.litcoffee` is just another possible extension for a valid Markdown document, unless I’ve misunderstood something along the way, and ideally should be rendered as such on GitHub.com.

Running the tests with `rake` failed *spectacularly* for me in ways that I imagine indicate that I’m missing something important that’s not in the README regarding bootstrapping the project (yep, I ran `bundle install`), so if these changes don’t work as expected, let me know and I’ll endeavour to change things accordingly.