Make "reattach-to-user-namespace" short and sweet

[forthrin]

Suggest making reattach-to-user-namespace short and UNIX-y. Currently, it really sticks out in the police lineup :)

$ brew leaves | awk '{print length, $0}' | sort -n
2 jq
3 ack
5 emacs
8 ddrescue
26 reattach-to-user-namespace

Right off the bat, the obvious runs and reuse both seem to be available.

$ brew search runs
Error: No formulae or casks found for "runs".
$ brew search reuse
Error: No formulae or casks found for "reuse".