Math rendering should work for reStructuredText

[Alhadis]

reStructuredText includes facilities for marking up mathematical expressions, just like GitHub-flavoured markdown does:

Syntax

	Markdown	reStructuredText
Block syntax	$$ ... $$	`.. math::`
Inline syntax	$ ... $	:math:`...`

Unfortunately, only Markdown gets to enjoy the properly rendered equations:

Rendered output

	Markdown	reStructuredText
Block syntax	$$\sqrt{3x-1}+(1+x)^2$$	\sqrt{3x-1}+(1+x)^2
Inline syntax	$\sqrt{3x-1}+(1+x)^2$	\sqrt{3x-1}+(1+x)^2

Since reStructuredText's uses MathJax's syntax for its equations, this should be a trivial fix on GitHub's end.