(WIP) 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 
I have implemented the code in the <code>dot</code> and <code>cross</code> methods only, and called them for the operator overloaders. In the tests, I had to put these expressions to test if the operator overloading is working right. I have included both kinds of tests - by calling the actual methods, and by using the operators.