Lenticuloid expansion

The good news:  This ends up being all that's needed for JSON lenticuloids (at least, I hope), since the `JSONArray` and `JSONDictionary` types can have their lengths changed with no real consequence.

The bad news:  The only reason I needed to worry about lengths at all is that `Traversal`s (and `PartialLens`es) turn out to be *completely unrepresentable* without higher kinds.  We'd need either the full `IxStore` transformer, or to swap the whole system over to van-Laarhoven "functorial" style.  The only other option, the residual representation, is right out because Swift doesn't have encapsulated existentials (and it only just barely has encapsulated universals, for that matter).  Until and unless Apple fixes these "feature issues", Swift will be fundamentally incapable of representing most of the advanced lenticuloids generically.

So we are left with a predicament.  What do we really want out of our lenticuloids?  Is this good enough, or should we look for alternative means of expressing things, perhaps by exploiting mutability?