Overloaded geometric step length calculations to handle 3D vectors.

Overloaded calcSlidingStepLengthToOrigin() and calcSlidingStepLengthToMaxChange() to handle 3D vectors, as requested by Sherm. Both methods are simple analogues of their 2D counterparts, though the latter contains an optimized computation sequence generated in Maple. Verified both methods against a handful of Maple test cases.