On html5lib maintenance

[akx]

Hi there!

#361 discusses funding for maintenance, but that conversation has languished a year and a half ago.

It looks like there's a bunch of PRs that would bring this repo a bit into the present (and into the future!), but there's... maybe no one around to merge them? Sorry for the ping, but @gsnedders, @jgraham, you seem to have been the last folks to merge PRs around here; would you need a hand maintaining things and getting things rolling again?

For clarity, my angle here is that I inadvertently caused a bit of havoc over at nbconvert by switching their HTML sanitization away from lxml.clean_html to bleach, which, as we know, uses html5lib under the hood, and there are some performance issues now; see jupyter/nbconvert#1892. Also, for the record, I'm no stranger to maintaining a popular PyPI package; I'm the current de facto maintainer of babel.