(WIP) Basic Vector framework

Added:

1. Vector core - Vector, VectorAdd, VectorMul, BaseVector
2. BaseScalar
3. Del
4. CoordSysRect
5. Point
6. functions.py - express, matrix_to_vector 
I agree. But usually the simplifications needed out of rotations and orientations are trigonometric in nature. Hence the implicit use of trigsimp - or am I wrong?