Convert TeX to XML and then to HTML

[eterps]

Addresses: https://github.com/guidoism/tex-oberon/issues/1

This is an attempt to start conversion of oberon.tex to XML an then to HTML.

I don't have enough knowledge of TeX related tooling, so this PR is just to demonstrate my effort (in case it's helpful to others) and a possible follow-up. The current attempt breaks at the first code example, the result can be viewed here:

https://html-oberon.surge.sh

Another approach might to be to use: https://github.com/phfaist/pylatexenc