&remind functionality

[Helzibah]

I'm bad at remembering stuff, do it for me?

Command: &remind 30m do the thing Expected result: 30 minutes later, <janebot> Helzibah: do the thing

where 30m is a parseable time duration; hours and minutes is base minimum, could just be done with '1h30m' and not worry about more expansive parsing. Beyond that, days, weeks, months or specific dates would be awesome but would start to require persistence in case of restarts.