Clean up `handle` function
Get rid of `RecordWildCards`
Proper registration/unregistration of addresses

Previously incoming connecting addresses were registered instead of the
announced ones. Now registration/unregistration is made with `bracket_`.
`NodeConn` is now a `MonadCatch` instance.

Also Map `connections` -> Set `peers`.
Update TODO
Demo program removes closed Unix domain sockets when a exception is raised