Additional Function Definitions

New definitions are made for the built-in Mathematica symbols Direction and Jacobian (options for Limit and FindRoot, respectively). The new functional definitions that are made for these symbols by MechanicalSystems do not interfere with their standard Mathematica usages as option names.
MechanicalSystems also makes additional functional definitions for Cross and Dot. These new definitions do not interfere with the built-in definitions, they simply allow Cross and Dot to automatically convert MechanicalSystems vector objects (Vector, Line, Plane) into normal vectors so that the cross or dot product can be calculated. Further, Modeler2D defines the cross product of a pair of 2-vectors, which is not defined by the built-in definition of Cross.