Added .ToArray() and .FromArray() for Vector types

This commit adds Vector2.ToArray(), Vector2.FromArray(float[]),
Vector3.ToArray(), Vector3.FromArray(float[]), Vector4.ToArray() and
Vector4.FromArray(float[]). The FromArray method copies the array elements
to a vector: the element at index 0 becomes X, the element at index 1
becomes Y and so on. The ToArray() method converts the vector to an array:
it puts X at index 0, Y at index 1 and so on.

These methods looked useful to me if you have an array but want to do
vector operations.