Generate the displacement of a node (Random Direction).
[X,Y,A] = NL_M_NodeRD(X,Y,A,V,L)
Node x-coordinate (current position).
Node y-coordinate (current position).
Node angle (current angle).
Node speed.
Area side.
NL_M_NodeRD generates the displacement of the node currently located in (X,Y) in respect with the random direction mobility model. On reaching the boundary each node selects another direction to follow.