Bug Fix: previously, if {sp:0} was passed to MagOrderingTransformation, the sites would be assigned a fraction of spin +0 and spin -0. When passed to the enumeration code these sites would appear as equivalent (+0 == -0) and the structure would be enumerated and this would result in partial removal of sp. New code exits if the structure is ordered after spin assignment. If ordered, now returns a list containing the ordered structure (with spin assigned to sites) if return_ranked_list is > 1, else returns the structure itself
testcase for zero_spin bug