Add combos

[qwelyt]

While OnHold lets you change behavior if pressed or held, and chording lets you act as a different key if more are held at the same time, combos act when you press keys in series.

Chroding: Press J and K at the same time to produce W.
Combo: Press J. Release J. Press K within time_limit and produce W.

So chording is pressing at the same time, and combos are pressing in the right order in short succession.