Support for Obj-C generics and type annotations

[rafalio]

Are generics and type annotations something you are thinking of adding to this package for Obj-C?

For example, it's now legal to do something like NSDictionary<ClassA*,ClassB*>* in Obj-C to annotate that the NSDictionary is parametrized over ClassA and ClassB. From my cursory look at the code it appears this is not supported.

[mchakravarty]

@rafalio I wrote the Obj-C support, and you are right in that the latest additions to Objective-C (basically anything from WWDC 2014-2016) are not supported. I don't currently have the time to do anything about that, but I assume that @mainland would be happy to include a contribution from somebody else.

[mainland]

I would be happy to accept a pull request.