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)
Once Coordinate systems come into place, they will become a part of the 'id' tuple. Currently, since everything happens in the same frame, the 'id' only includes the index.
The reason why the name isn't included in the hash, is to enable a user to have different names for the same BaseVector all of which are 'equivalent' because they correspond to the same (coordinate system, index) tuple.