Resolve macros in LaTeX files before detecting entities

cc @dykang @kyleclo

To aid in definition and symbol detection, macros should be expanded in LaTeX files before they are processed.

I haven't had much luck so far finding a tool yet for expanding macros. Options seem to include:
* `de-macro`: a command line utility that will expand commands defined with \newcommand (though not \def)
* This script (https://tex.stackexchange.com/a/11236/198728) (also only works for \newcommand, I think)
* A home-brewed solution

(source: This TeXExchange question: https://tex.stackexchange.com/questions/3174/latex-macro-expander)

For the home-brewed solution, there are a couple of options.

1. if `\tracingmacros=1` is set at the beginning of a LaTeX file, then LaTeX will output expansions for each of the macros called. During compilation, it might possible to do a first compilation pass to get the macro expansions, and then replace the macros with their expansions before the next pass.

2. support a subset of macros (e.g., those with very simple expansion patterns), and write our own scanner that finds these macros and expands them in the files. I expect this might be the 80 / 20 solution (e.g., the one where we only have to spend 20% of the work to get 80% of the payoff).