Add support to mathjax style

[uoyniXnaH]

Resolve #514

[uoyniXnaH]

I would like add some information. I found that if I add rehype-katex and rehype-mathjax at the same time, the formulas may be rendered three times. So I keep using katex, only to replace delimiters like \[ to $$, thus those mathjax expressions could be rendered by katex.