This is similar to lasagna but with strongly typed elements. Let's see how it goes.

Support for type erasure of views and widgets.

Bring in more widget tuples with a macro.

Event propagation has no mutable access.

This passes the app state down through an Rc using a lens-like construction.

I'm not sure this is the best construction. Perhaps it should be combined with adapt (the callback could take both mutable state references), but that's 3 callbacks.

Also makes state mutable in event propagation, which seems useful.

Also trying out a few more node types in the example.

WIP

Implements the bones of integration with async, including routing a wake event to a node in the view tree.