x-ship spin in radians; changed add-seconds of timer to set-seconds
cleaning up
map-coords non-consing
map-coords bf: screen-width used for screen-height.
using regular timer for missile lifespan
eliminated rock's pos (mob already has one); original rocks are placed randomly.
standard timer for powerups
made ship more sluggish for better gameplay
made ship more sluggish for better gameplay
made ship more sluggish for better gameplay