switch docs math to mathjax

[elbeejay]

This closes #265 by switching the sphinx extension from generating images of the math to generating them using the JavaScript mathjax package. There are other math rendering options built into sphinx (https://www.sphinx-doc.org/en/master/usage/extensions/math.html) that we can switch to if/as the need arises.

Math is now displaying properly in my local builds.

[codecov[bot]]

Codecov Report

Merging #266 (89b62f3) into develop (f9951c6) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #266   +/-   ##
========================================
  Coverage    78.82%   78.82%           
========================================
  Files           11       11           
  Lines         2611     2611           
========================================
  Hits          2058     2058           
  Misses         553      553           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.