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 
Body fixed rotations are described by three angles and three body fixed rotation axes.  To orient a coordinate system D with respect to A, each sequential rotation is always about the orthogonal unit vectors fixed to D. For example, a '123' rotation will specify rotations about D.i, then B.j, then B.k.This is equivalent to:

```python
A = CoordinateSystem('A')
B = A.orient_new('B, 'Axis', q1, A.i)
C = B.orient_new('D', 'Axis', q2, B.j)
D = C.orient_new('B', 'Axis', q3, C.k)
```

Body fixed rotations include both Euler Angles and Tait-Bryan Angles, see http://en.wikipedia.org/wiki/Euler_angles. 

Space fixed rotations are described by three angles and three spaced fixed rotation axes. To orient a coordinate system D with respect to A, each sequential rotation is always about A's orthogonal unit vectors. For example, a '123' rotation will specify rotations about A.i, then A.j, then A.k.

```python
A = CoordinateSystem('A')
B = A.orient_new('B, 'Axis', q1, A.i)
C = B.orient_new('D', 'Axis', q2, A.j)
D = C.orient_new('B', 'Axis', q3, A.k)
```