Keeps track of and adds callbacks for when players press, hold, and release controls
original forum post: https://forum.minetest.net/viewtopic.php?t=18471 original author's gamer handle:
Arcelmi
original github: https://github.com/Arcelmi/minetest-controls/
CHANGES BY MisterE:
Updated to be compatible with MT 5.3, which has a zoom key, which was causing a nil value error.