Now using a physical stage in the hope that bullets will fly using Chipmunk logic
Bullet has mass now.  Trajectory appears a little off...but we'll see how that goes
WIP: commented out some code while testing
Bullets are firing correctly!

* Using Chipmunk's vectors and CP::Body#apply_impulse. This means:
  * http://beoran.github.com/chipmunk/
  * bullets fly in the right direction all the time
  * I don't have to use horrible, hand-rolled, broken trajectory system. :)
* No collisoin detection yet.