Include the required supertype in interface declarations

[rafaqz]

I'm thinking it may make sense if interface declarations have to include the required supertype, like:

@interface SomeInterface SomeType conditions docs

For interfaces without supertypes, like iteration, this would be Any

@interface IterationInterface Any conditions docs

Originally this was not included because the Any case is redundant. But now I think it might be nicely self documenting -
wherever there is Any its a trait only interface.

@gdalle any thoughts?

[gdalle]

I like that idea! And it's probably a minor code change