CircleBug Exercise

Added working version of the CircleBug class actor, which moves in a rough
circle (an octagon, actually), as well as a Runner for said Bug.
DancingBug Excercise

Added working version of DancingBug, which 'dances' in a specified pattern given
by how many turns to make after each step, as well as a runner for said Bug.
SpiralBug Exercise

Added working version of SpiralBug class actor, which traces out a square spiral
of steadily increasing radius, equivalent to twice the given side-step argument,
and a Runner for said Bug.