[tex4ht] Lua parser for HTF files

[Michal Hoftich]

Hi all,

Nasser pointed out one issue with conversion of Unicode characters
inside \Picture* \EndPicture command [1]. The problem is that the
Unicode values are stored in \special commands followed with bogus "x"
characters. I've provided detailed explanation in my answer [2], so I
will not repeat it here. The point is that I've created a Lua module
for HTF file parsing (it is included in the answer). It can be used in
the way I explained on TeX.sx, but it can be also used in the other
way - for conversion of 8-bit font glyphs to Unicode.

This was a limitation I've found in my experiments with producing HTML
directly from LuaTeX using Lua callbacks, it was possible to get
correct characters only for OpenType fonts. This was a huge drawback
especially for math.

We should add the functionality provided in the answer to tex4ht by
default, but some testing before would be nice.

Best regards,
Michal

[1] https://tex.stackexchange.com/q/448564/2891
[2] https://tex.stackexchange.com/a/449022/2891