Add GitHub Flavor Markdown support

[the-rccg]

Expected Behavior

I am currently including my readme markdown file in the documentation to make sure all information is up to date whenever it is changed in the readme.
Specifically, it is done in the init.py via the docstring and used to generate HTML
"""
.. include:: ../../README.md
"""

Actual Behavior

The "include" does not display certain things properly:

1. Lists do not seem to work, which is weird
2. JPG images, although it does seem to plot SVG images.
3. Certain features like latex \begin{align} do not work and cause linebreaks to be removed
4. Latex in Tables doesn't seem to work

Quick links to the example at hand:
documentation: https://the-rccg.github.io/hw2d/index.html
github readme: https://github.com/the-rccg/hw2d

Additional info

Specification of GitHub Flavor Markdown: https://github.github.com/gfm/
Previous Maths display issues: #70
Seems to also be related to this issue: #269
However, some of the problems at least seem to be specific to the include as it does not render Lists or images that should be standard markdown behavior? I'm not too familiar with the different flavors and only now getting started looking into this.

[MrNickArcher]

I just ran into latex \begin{align} not working. :(

It was a bit hard to find this pre-existing issue with all those problems lumped together. I get the impression that mathjax support is a separate thing with its own CLI flag. Maybe it should be its own issue?

[thehappycheese]

May be related to #158 ?