Fix MathJax gimmick

* Add inline configuration for MathJax
* Use ```math ``` in code blocks to indicate math content
* Inline Math is now triggered by $$ ... $$ but stil lsubject
  to a bug where the content is inside the $$ is processed by
  our markdown parser
* Non-Inline math can be instered with the triple: $$$ ... $$$
  notation but subject to the same bug
* => better use ```math for now