Rewrite that changes method of determining permission inheritance among objects. Adds mapping table PermissionAncestor. Adds methods to 1) determine permissions using joins to PermissionAncestor and 2) to populate PermissionAncestor as needed when PermissionableObjects are saved. Test are now broken. :(
Adds custom save method to PermissionableObject that updates PermissionAncestor records.
Update README, some clean up of code formatting.