Automatic source code insertion

I made this fork to enable something I always use for my implentation of kss-rails, it adds a source code sniplet to every `styleguide_block` in the style guide:

![example-with-code](https://f.cloud.github.com/assets/167882/104556/c8e98c72-6988-11e2-99d4-e05a6777274a.png)
 
I styled the source code with [Rainbow.js](http://craig.is/making/rainbows/)