[XeTeX] tex2utf: updated tex2mail to read/write unicode rather than ascii

[Mike "Pomax" Kamermans]

Hey all,

I don't know if this is still useful to folks in 2020, but I was looking 
for a way to embed all the LaTeX maths I'm using on my Primer on Bezier 
Curves (https://pomax.github.io/beziercurve) as code comments/fallback 
and after trying the various "latex to plain text" tools I could find 
(they're hard to come by, and it's a short list: asciitex, catdvi, 
tex2mail, pandoc, tex4ht, and those last two were long shots), the thing 
that got closest to at least usable was tex2mail, which turned out to be 
not too crazy hard to massage just a tiny bit into working reasonably in 
modern contexts where even the default monospace fonts have ridiculously 
wide unicode support.

On that note: all credit to Ilya Zakharevich, I haven't worked with Perl 
in 20+ years but the tex2mail code is organized well enough to allow 
folks to pretty quickly jump in an update it.

So I did: I've updated it to suit at least my own needs and stuck it 
online as tex2utf over on https://github.com/pomax/tex2utf in case 
anyone else could use a utility that turns (a surprisingly large amount 
of) (Xe)LaTeX maths into plain text form. And if anyone wants to help 
further massage it, or come up with a github action that autosubmits 
releases to CTAN, do let me know.

- Pomax