Misc changes and fixes to multipolygon hole determination, add shape geo interface testing

Move all multipolygon hole determination to separate organize_polygon_rings() function.
Fixed buggy point-in-ring algo.
Switched away from buggy sample_ring points, to full ring in ring containment test.
Switch to simpler area-based determination for nested exterior-holes (which is how gdal also does it).
Switch geo interface to consistently returns lists instead of tuples.

Author: karimbahgat