Add simple Tex support

[walking-octopus]

Motivation

Many do not imagine Markdown without inline TeX. ASCII Math can get you surprisingly far but becomes rapidly unreadable with more advanced notation.

Alternatives

I suppose using one of many web services that dynamically render the TeX from hotlinked URLs is already supported but slow and breakable. Rendering it yourself and embedding in images is annoying. Thus proper TeX rendering in the viewer is the best option for math heavy documents.

Implementation

tectonic implements most of simple TeX, so may be best fit for this usecase.