[tex4ht] htfgen testing

[Michal Hoftich]

Hi all,

I've added some documentation to htfgen

https://github.com/michal-h21/htfgen

this is a tool to generate htf files for tex4ht, this task is even
more difficult than I thought, but I was able to make working htf
files for standard text fonts. The main difficulty are math and
virtual fonts, it seems that lot of hand editing will be needed for
math fonts, as their encoding files often doesn't provide useful
information.

Michal