Updated RayCast() function.

Added a RayCastContact struct to PhysicsCore.h that will be used to
store information about the collision detected during the ray cast.
Added pass-by-reference parameter to RayCast() function of type
RayCastContact so the function can pass back information about the
contact that occured, if any. Reworked RayCast() function from the
ground up to support returning the appropriate information.