Added support for an additional options hash that gets passed to a syntax highlighter
Math engines are configurable now

* The only math engine implemented right now is MathJax for
  the HTML converter.

* As with the syntax highlighters, there is an option math_engine
  for specifying the engine itself and an option math_engine_opts
  for specifying options.
Updated syntax highlighter documentation

* Added information on Rouge
* Some fixes in Coderay documentation