Ant-based annular sorting

Annular implements Martyn Amos' ant-based annular sorting algorithm. The population consists of moving ants (the red and green dots) and various sizes of static eggs (the white circles). Ants can make aesthetic judgements about the placement of eggs. When an ant encounters an egg that it feels to be poorly-placed, it picks it up and carries it until it finds a better location for it. Using a simple aesthetic rule, the ants can eventually sort the eggs into rings by size, with the smallest eggs in the centre and the largest at the outside.