Feature: Option to activate only if released within time

[hirak99]

Add an option to apply the key only if it is released quickly.

So instead of -

DELETE+nothing=DELETE

We should be able to have -

DELETE<500ms=DELETE

Note that implementing this will not require threading, so should be relatively simpler. (However, implementing the reverse, i.e. do something if a key is held for stipulated time, will require multiple threads.)