add asteroid courtesy properties for the x and y positions
provide an ASTEROID_SAFE_ZONE where explosions can't destroy them. Fixes a bug where explosions high enough chain-react on incoming asteroids.
turn off music
load the sprite sheet and draw puzzle phase sprites
comment code to scale puzzle sprites
reduce puzzle area size
remove unused sprite code
load and rescale sprites into a dictionary for easier reuse
use sprite's built-in draw methods
add sprite sheet
load gun turret sprites