Rendering code blocks with CoffeeScript highlighting if the file is of type .litcoffee; closes #129

Closes #129 
This probably shouldn't go off the extension but instead use the grammar for the current editor.  There are multiple literate coffee extensions: https://github.com/atom/language-coffee-script/blob/2f44f55c2c41c3db0dcde50555d8f195249bf38d/grammars/coffeescript%20(literate).cson#L2-L6

It should instead check for a grammar with a scope name of `source.litcoffee` that is available by calling `editor.getGrammar().scopeName`