rose documentation: add syntax highlighting (via Google Code Prettify)

This adds Javascript-based syntax highlighting to our documentation, courtesy of <a href="https://code.google.com/p/google-code-prettify/">Google Code Prettify</a>.

I found the Google one to be better than the similarly-powerful <a href="http://alexgorbatchev.com/SyntaxHighlighter/">SyntaxHighlighter</a>.