* add rock1, rock2, rock3
* add particles spark1, magic1, flies1
* add HUD labels top, center, bottom
* better gameplay

FIXME: particles are CPU consuming :-/
* add particles emitters

FIXME: emitter parameters are a bit square?
* add game restart when hud bottom label pressed
* add test if energy > 0 to launchMissile
* add touchesEnded method to handle user commands on HUD