Enable math env like github flavoured markdown.

[bvraghav]

Writing expressions as blocks

For example, with markserv, the following math (code?):

$$y=mx+c$$

would render like

y=mx+c

Would it be possible to append custom block delimiters with mathjax?

Some pointers:

1. MathJax Config: {tex: {displayMath: [['$$','$$'],...,['```math','```']}}
2. Insert a script tag here.