Please implement Vector<T> From<Point<T>> trait

[MillieFD]

The From<Point3<T>> trait is not currently implemented for the Vector3<T> struct. Attempting to add this implementation in my own code causes complier error E0117 (Only traits defined in the current crate can be implemented for arbitrary types). It is therefore necessary to implement this From trait at source.

As the Point struct is based on the Vector struct, this should be very easy to implement.

[sebcrozet]

This looks like a reasonable addition.