Update agentscript to latest merged master

Note, this will break existing models. Next commit updates
the models to make them work with current version.
Update models to latest agentscript API.

Changes required for these models:

 - @agentsetName is no longer a function
 - Cannot set breed after creation, must either create with @agentsetName.create or
   change an existing agent with changeBreed. Note that changeBreed returns a *new*
   agent of the new breed with the same xy coordinates
 - New anim property contains ticks and frame rate

I haven't yet studied the new animation functions enough to understand the rate 
properly. It may just be a frame rate, not anything that governs the model step rate.