Use MathJax

Used ideas from
- http://drz.ac/2013/01/03/blogging-with-math/
- http://drz.ac/2013/01/14/matching-content-to-mathjax/
- http://brianbuccola.github.io/blog/2012-11-28-latex-math-in-octopress.html
and org-mode source
new test post