hplot: consider implementing a "full" LaTeX parser engine

[sbinet]

so we have nice LaTeX formula support, akin to matplotlib's mathtext:

• https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/mathtext.py

[sbinet]

alternatively, one could also consider a "troff"-based engine (might be easier)

• https://github.com/sevki/troff

or a markdown+mathjax:

• https://github.com/yuin/goldmark
• https://github.com/litao91/goldmark-mathjax