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 
SymPy's `S.Zero` is declared as

```class Zero(with_metaclass(Singleton, IntegerConstant)):```

did you try this one (maybe without `IntegerConstant`)?

By the way, it doesn't seem terrible that the hash be zero, just consider that `hash(0) == 0` in Python.