female ninja shurikens

both players can now fire shuriken. left uses SPACE and right uses
SHIFT.  Shurikens destroy eash other onhit but are not mutually
destructive. (one shuriken will prevail over the other)
Shuriken fix and point/health system implementation

Shuriken will now destroy after traveling a certain distance without
colliding with anything. fixes game performance.

on hit with player, opposing players points go up as the hit players
health goes down. will probably want to transition to using only health
bars.

need to work on stopping th game after one player makes the other
players health go down.
also need to fix player boundaries so the player cannot walk out of
frame.