Better Collision Testing and Unit Vectors

I noticed that one might want to have collision detection within a
specified distance from the Plane. Also, I created a method that returns
the "Unit Vector" of a vector, which is basically the same Vector, but
with a magnitude of one.
Improved Simulation Accuracy

The simulation now uses the nanosecond-level timer that the System class
provides to improve the level of accuracy of the physics calculations.