add ZQ to quit without saving

[xfnw]

ZZ or :wq quits and saves, but there is no key combination for :q! quit without saving. this pr adds vim's ZQ key combination to quit without saving.

i know a lot of vi implimentations do not have this, but it is nice to have and is not very big.

[brentr]

Your patch looks fine... however...
The ZQ sequence discards all changes without feedback to the user.
I completely understand why the original author this vi clone choose to omit it.
With the :q! sequence, you can see the keystrokes on the command line as you type them.
Granted, it is two more keystrokes. I'm OK with that to avoid the prospect of losing hours of work.