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)
Dummy/Symbol's <code>\_\_new\_\_</code> method does not take more than one arg. As it is, I would be pushing this all in _together_ with CoordSysRect. In such a case, the 'name' of a BaseScalar would be like 'system.x'...so it would be unique.