Use sphinx-math-dollar for Math formula in API documentation

Just found sphinx-math-dollar from this post: https://www.asmeurer.com/blog/posts/quansight-labs-work-update-for-september-2019/ .

Currently, the API documentation of GAlgebra splits into two scattered pieces:

1. The old doc on the API converted from @abrombo 's original doc in LaTeX, it’s great but it’s somehow outdated (@abrombo has some updates on the doc and yet to be merged )
2. The API document automatically generated from docstrings in code but it’s mostly ill-formated.

1 is at https://galgebra.readthedocs.io/en/latest/galgebra_guide.html#Module-Components 2 is at https://galgebra.readthedocs.io/en/latest/api.html .

The scenario causes maintenance burden and one of the reasons why @abrombo preferred to work on a separate repo is that it’s difficult to maintain LaTeX doc and Sphinx doc (but there wasn’t such an automatic API doc back then) at the same time.

By ill-formatted, I mean:

It’s still parseable but cumbersome. I was aware of this situation but I felt unwilling to rewrite them in the verbose syntax of reStructuredText so I left them there and treated them like plain text.

Now, with the help of sphinx-math-dollar which SymPy is also using, the situation can be fixed. So I opened this issue to add this work to the backlog.

However, this does not solve the maintenance burden issue which I only mentioned it as a context and comments and suggestions are welcome @abrombo @hugohadfield @eric-wieser .

[eric-wieser]

I suppose either is fine - my point was that the dollar support is purely a convenience thing, and the latex rendering can be obtained with or without it. If the convenience is valuable, then by all means use it!

(Having said that, I just configured my editor to render :math: inline so am now biased)

[asmeurer]

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