OrderedMultiSet and OrderedSet now implement +/- operators
OrderedMultiSet and OrderedSet now implement +/- operators

CosmicMind/GraphKit,CosmicMind/Graph,GraphKit/GraphKit,CosmicMind/GraphKit,GraphKit/swift,GraphKit/swift,CosmicMind/Graph,adamdahan/GraphKit,adamdahan/GraphKit,GraphKit/GraphKit-swift,GraphKit/GraphKit-swift,GraphKit/GraphKit