added immutable results for all concurrents operations
Update README to indicate support for NSMapTable
Merge pull request #3 from seanlilmateus/feature-immutable-results

Conflicts:
	ConcurrentCollectionOperations/NSArray+ConcurrentCollectionOperations.m
	ConcurrentCollectionOperations/NSDictionary+ConcurrentCollectionOperations.m
	ConcurrentCollectionOperations/NSSet+ConcurrentCollectionOperations.m