Support inline and display math through delimiters.

[veillette]

ideally we would support math delimiters through a mathjax config rather than relying on css block.

  inlineMath: [              // start/end delimiter pairs for in-line math
      ['\\(', '\\)']
    ],
    displayMath: [             // start/end delimiter pairs for display math
      ['$$', '$$'],
      ['\\[', '\\]']
    ],