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 
A better way would be to return tuples of 
(base_vector, base_scalar) for each 'dimension' which is being iterated over. Thoughts?