Use another QuadTree impl. from https://github.com/mikechambers/ExamplesByMesh/tree/master/JavaScript/QuadTree
Code cleanup, accessors conformity.
Annotations use the quad tree for -annotationsInMapRect: method.

Notes:
Annotations and overlays do not currently use a quad tree for reusing google overlays as needed but it should be possible to do so.
Some of the code needed for managing reuse of overlays is commented in MKMapView.j