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 
VectorZero needs to inherit from Vector.
So will it go as
<code>class VectorZero(vector, with_metaclass(Singleton))</code>?