(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 
These are default names. If the user wnats to enter his own names, he can do it in a list with the parameter <code>vector_names</code>. These names like <code>C.i, C.j, C.k</code> will only be set if the user does not enter his custom names.