Basic vector code, without a coordinate system class

All calculations essentially occur in the same frame.
i, j, k and x, y, z are imported as base vectors and base scalars by default on importing sympy.vector.
delop is a Del operator instance.

Example:

>>> v = 3*i - j
>>> delop ^ v
0

(delop ^ v represents curl of v)
I am looking at the diffgeom code. Maybe I will copy parts of the code. But for the use cases that the vector module is designed for, integrating the classes from diffgeom module into sympy.vector doesn't seem that good an idea.