Bug fix: Reduced collision bounce to minimum distance. Added unit test to test it.
Minor code cleanup
Updated inline documentation and moved unit tests into test dir

Also fixed a small bug where velocity wasn't reset when clearing
waypoints in LinearParticle
Added goal_occupied convenience method

* Updated Arty to use goal_occupied to avoid time consuming searches in
impossible states.
* Added BestToFollow scenario demonstrating another scenario where Arty
works better than non-predicting algos.
* Fixed add_walls-logic in Scenario baseclass