Problem

I don't use Texlive, I use Tectonic, and I using plt.rcParams['text.usetex'] requires me to download a different LaTeX engine, not only because the latex binary is searched, but also because the tex files that are meant for compilation are meant for pdflatex, and not xetex, which tectonic essentially wraps.

Proposed solution

Add a new option to rcParams which will enable using a different LaTeX engine, and another option that will control whether the generated tex files should be intended for xetex or pdftex.

This seems not too complicated to solve, but I wish to know what do you think, and whether you'd be willing to add more moving parts to TexManager class, especially since the generated tex files for a xetex engine should be substantially different.