Behavior namespace

[ethanmusser]

All of the kodlab::Behavior-related code (i.e., Behavior, IOBehavior, BehaviorManager from #40, and MjbotsBehaviorLoop from #41) should move from the kodlab namespace to a behavior-specific namespace, perhaps kodlab::behavior. Additionally, these files could all be moved to their own subdirectory of include.

See discussion in #40.