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 
There needs to be something in the doc string that clarifies which form of the dcm is returned.

For example, if there exists a vector v and v_a represents v express in the A frame and v_b is v expressed in the B frame, then are you creating R for:

v_a = R * v_b

or

v_b = R * v_a

You can say it this way too. If v is a vector in A and I want to rotate v such that it is oriented in a different direction in A and is aligned with w which is the same magnitude as v, are you supplying:

w = R * v

or

v = R * w