PortalPutt v0.2.1

Physics improvements and netspam reduction

Partially-obstructed portals are now handled more stably and
consistently, and the ball's position is now maintained more accurately
between portals regardless of their orientation.

Added a check to reduce netspam from stationary golf balls sitting on
top of portals.

PortalPutt v0.2

Quick bugfix

Portal collisions failed to detect at high altitudes when using the
position vector to check for them. Switched to using the step
algorithm's impact point instead.