[Python-3000] Abilities / Interfaces

[Andrew Koenig]

> Hm, I would think it extends very naturally to instance variables, and
> I see no reason why it's a particularly bad idea to also extend it
> (mostly in our minds anyway, I expect) to describe certain behaviors
> that cannot be expressed (easily) in code.

I think of an ability as a property of an interface rather than an interface
itself.  For example, I can imagine a single interface having multiple
abilities.