Sanitize bot output

[slushiegoose]

Fixes #1031

This removes the argument from the BadArgument command and runs filters over !eval output, as requested.

[sco1]

This only fixes one possible path in the error handler, not all of them, and also has missed the docs cog. Forget it

[slushiegoose]

This only fixes one possible path in the error handler, not all of them,

this is the only path that repeats the argument

also has missed the docs cog.

lemon mentioned in #1031 (comment) that the docs don't actually circumvent it very efficiently so it isn't really a problem

[lemonsaurus]

I think this is more or less a complete solution. There may be edge cases that aren't caught by this, but it's a big enough step in the right direction that I'm comfortable moving forward with it.

The code quality is quite excellent, too. Nice work.

Never mind

[lemonsaurus]

@slushiegoose Can you sort out the failing test?

[MarkKoz]

Great work. Thanks!