Drop the formatting addon

It's flaky, and I don't want to support it.

Everybody: feel free to take the code, put it in some other repo
and maintain it.
Remove mysql and plsql modes

Use the generic sql mode, which has MIME types for these dialects.
Split folding functions into their own files
Remove the collapserange addon

Too specialized. Out of scope.
Remove simple-hint addon

Use show-hint, which is much more solid and configurable.
Mark release 3.11
Bump version number post-3.11