Represent agents as cartoon children

[drphilmarshall]

How hard can this be in matplotlib? ;-)

[mbaumer]

Looks like there's no elegant way, but this kludge looks like it will work with our animation framework (since it manipulates the "line" object.
http://stackoverflow.com/questions/2318288/how-to-use-custom-marker-with-plot
There are some annoyances with image pixels vs. grid pixels, but I should be able to work it out