Agent2d / dimensionality

Originally, I intended for this model to be a Java3d model. Besides being whizzy, a realistic model of people interacting benefits from more personality dimensions. Unfortunately, it soon became clear that explaining that code would be too hard for this purpose.

What I did instead was to organize the parts of the code oriented toward 2d and 3d into different packages. In fact, most of the code in the model is oriented toward 2d interactions. This is the kind of realization that is often not obvious to modelers who write a simulation. Coming up with a general notion of something like `interaction' can be hard.

The code relevant to the discussion that follows can be found in `agent2d', which corresponds to the Java package of the same name.