The tank demo displays two tanks and some obstacles.  The tanks
make little sparkles when they blow up, but then reappear.

To run the demo, type the command:
        .EX SPCWR3

Control is via the switch register:

Right 2 up	Tank 1 drive backwards
Right 2 down	Tank 1 drive forwards
Right 3 up	Tank 2 normal
Right 3 down	Tank 1 steer left
Right 4 up	Tank 2 normal
Right 4 down	Tank 1 steer right
Right 5 up	Tank 1 fire cannon
Right 8 up	Tank 2 drive backwards
Right 8 down	Tank 2 drive forwards
Right 9 up	Tank 2 normal
Right 9 down	Tank 2 steer right
Right 10 up	Tank 2 normal position
Right 10 down	Tank 2 steer left
Right 11 up	Tank 2 fire cannon