Added the fundamentals of charging an entity contained in a turret. The concept
of the charge is that it is a percentage that goes from 0 to 1 over X amount
of time. Also there is a symmetric decay that can happen as well. Fixed
spawn to take a new keyword EXTRA-INIT so I can pass additional init
arguments when spawn calls make-instance. This allows me to transfer the
charge the muzzle has to the instance of the thing it fired.
The turret can have any payload, not just a muzzle, so fix the symbol
names so I don't imply something that isn't true.