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 never liked this API. It'd be nice, in my opinion, if it were `A = N.orient_new('A', 'Axis', q1, N.i)`