Added the first real feature using charged weapons.
Added apowerup that is a downward facing arrow. Getting the first
one enables a charge effect with a 2.0 second delay when holding
down the space bar to full charge. Each downward facing arrow power
up acquired after tha decreases the charge time by 1/2. So the first
powerup is 2 seconds charge, the second gotten is 1, the third .5
the fourth .25, etc.  The effect of the charge is that depending how
fully charged the shot is, it will emit 1 to 5 additional uncharged
shots when the original shot hits something and is not absorbed.