Add registered user class (incomplete) and clean up docs.

Look, I did this like two years ago and never committed it. I really
have no idea what's going on. Apparently I started on a registered user
class and I fixed a bunch of typos and for some reason some MemoServ
tests started failing and I don't know why so I commented out the tests.

Limit max sequel version to 3.28.0 because newer ones break stuff.
Fix a missing `.chr` for 1.8.