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 don't see a use case for that. Currently, its just used as a part of a vectorial expression - rather than a 'function' of vectors. We could define special pretty-printing/LaTeX methods for it. But unevaluated expressions I am skeptical about.