Option for 2D vectors

[kolibril13]

At the moment, vectors have to be always 3D like [2,3,0] or np.array([2,3,0]).
What do you think of an automated behaviour, that adds a 0 to a 2D vector automatically, when a user gives a 2D vector?

[leotrs]

I have also found this to be annoying in the past. However, note that if we are going to make every function accept either 2D or 3D vectors, we should do so carefully so that we don't incur in runtime penalties.

[kolibril13]

Good point.
We could also make 2D vectors default, and add the optional flag three_d_vector= False, which can be set to true when going with 3d scenes