Issue 65 coderay pygments

This PR adds the possibility to use coderay or pygments for source highlighting as an alternative to highlight.js.
If `:source-highlighter: coderay` or `:source-highlighter: pygments` is defined the reference on the highlight.js script is omitted.
Additionally the CSSs for coderay or pygments are added (just like in the html5 backend! ;-) )