doxygen + sphinx + readthedocs - C++ and Python test

Motivation: have documentation build for both C/C++ and Python in one documentation set. To do this, we'll use Doxygen and Sphinx.

We basically just need to follow the following:

1. Format docstrings according to accepted formats
2. Setup Exhale according to the Quickstart guide

Exhale sets up Sphinx to call Doxygen to deploy to readthedocs.

Proposed format

The key part is the second * on the first line. This is what tells Doxygen this is a docstring. There are other formats, but this one is easy. If you have a strong opinion, let me know

/**
 * A brief history of JavaDoc-style (C-style) comments.
 *
 * This is the typical JavaDoc-style C-style comment. It starts with two
 * asterisks.
 *
 * @param theory Even if there is only one possible unified theory. it is just a
 *               set of rules and equations.
 */
void cstyle( int theory );

Things to note

Exhale just sets ups Sphinx to call Doxygen. So we still need to call sphinx. The first time you run sphinx in a project, you'll first need to run

sphinx-quickstart

and fill out the prompts. Then, modify the conf.py according to what Exhale asks for, add the requirements.txt, and update index.rst

Finally, you can make the docstrings by calling make html in the docs folder. Sphinx created a makefile when we executed sphinx-quickstart.