change private variables vx, vy, x, y, and color to protected variables for easy access in subclasses
OverlapBlip class created

Changes color based on number of blips on the same space.
Registry created

bad form used for quick prototyping
implemented overlapCount() using Registry.blips
MinimalistBoard shares blips ArrayList with Registry.

Note that this ad-hoc solution will fail when there are more than one board.
moved MinimalistBoard to io.shwang.blipworks
added preupdate() and postupdate() to update loop
start count at -1 so return value doesn't include overlapping self
create OverlapBlipTest