Converting non-english anchor tags leads to "-x" values (or umlauts are replaced)

[HardMax71]

Converting non-english anchor tags leads to "-x" values (or umlauts are replaced)

[Crozzers]

Seems to be a problem in the _slugify function where we encode all chars as ascii and ignore all errors.

python-markdown2/lib/markdown2.py

Line 2846 in 958eea4

value = unicodedata.normalize('NFKD', value).encode('ascii', 'ignore').decode()

Git blame shows this was last touched April 2012, so I guess this was a compatibility limitation at the time? The wiki page also explicity says header IDs are ASCII.
@nicholasserra can you see any issues with bumping this up to utf-8?

[nicholasserra]

I have no idea what the effects might be. If we switch and do some proper testing I don't see any reason not to.