Support additional collection classes

[dgelessus]

We already support NSArray and NSDictionary. Additional candidates would be:

• [ ] NSFastEnumeration, for generic iteration support over any Objective-C collection
• [ ] NSSet
• [ ] NSCountedSet
• [ ] Less common, more specialized collection classes? Not sure if these are all that useful.
  • [ ] NSIndexSet
  • [ ] NSOrderedSet
  • [ ] NSPointerArray
  • [ ] NSMapTable
  • [ ] NSHashTable