`str_utf8_isspace` now returns true if the passed code point renders as
a space, instead of when not.
Add `str_utf8_trim_right`, use this function and
`str_utf8_skip_whitespaces` in the server.
Add tests for the three functions
This uses the Unicode confusable data together with judging how close
two strings are by using the Levenshtein distance.
Adds the commands `name_ban`, `name_unban` and `name_bans`. Kicks
players who join using a banned name and doesn't allow ingame players to
change their names to the banned ones.