agents and agents2 must have the same number of agents/locations
or if different, one of them must have only one agent/location. If
agents and agents2 have the same number of agents/locations,
the directions are calculated for each pair agents[i] and agents2[i]
and not for each agents towards every single agents2.
If torus = FALSE, world does not need to be provided.
If torus = TRUE and the distance from one agents to
its corresponding agents2 is smaller around the
sides of the world than across it, then the direction to agents2
going around the sides of the world is returned.
The direction from a patch to its location returns 0; the direction from
a turtle to its location returns the turtle's heading.