Adapting bounding box tracker to a more general 'shape feature' tracker.  So far it uses the object centroid and area, and checks whether they are within threshold values in order to track an object from one frame to the next.
Normalized angles from cv2.minAreaRect so that they can be used as a third criteria in the ShapeFeatureTracker.
Added pruning of objects tracked for less than 3 frames.
Added freezing of objects that have not moved much and whose area has decreased (they are melding into the background).  Also added pruning of objects whose bounding box is completely within anothers.
Added pruning for highly overlapping objects (based on bounding box).
Working on method to detect leaving objects and increment counter.  It is having trouble with fish swimming right at border (towards border at some points) but not actually leaving.