[tldoc] html + \Thanh updates

[Karl Berry]

Eitan released a new version of tex4ht with some bug fixes I requested.
He also sent a new definition of the \Thanh macro that generates the
preferred ế for that double-accented character.

I've regenerated and committed PDF and HTML for English, German, Polish,
and Russian, although I can't really check the non-English results.
Please do so as appropriate.

Of the others:
Czech - awaiting final checks + sources from Petr/Jan.
Chinese - I was too scared about corruption to touch it; jjgod/yuewang,
  please check if anything is needed.
French - seems Daniel was already using Unicode.

Thanks,
Karl