Greatly simplified CocoaAMF module with tests without client and other tools

[jameshartt]

Not expecting this to be merged (as you're no longer supporting the project) and it removes a bunch of stuff to simplify things. It's more of a token of thanks.

But I decided to upgrade the core library and tests so they work in Xcode today.

This project has greatly helped me understand the now dated AMF serialisation for an implementation in Swift using the new Codable.