Pretty print

This pull request simply adds a `noHighlightCSS` config option to leave out the code highlighting style sheet (useful if using a custom style-sheet to avoid needing higher specificity to override the defaults).

I also split out the google-code-prettify code from the `highlight.js` file, and update it to the latest version.
The latest version now registers as an AMD module (in the same way as jquery), so utilize that fact rather than relying on the globals. 

Unfortunately, because it self-registers like jquery, it must be referenced with the name `google-code-prettify`, which dictates the file name and location unless the require.js `paths` feature is used.

I'd also like to add the `lang-css.js` auxillary file to allow for highlighting CSS fragments. However, I'm not entirely sure where to put that. Should it go in `js/core/`, in `js/`, or somewhere else?