Adding CONNACK data to the 'connected' callback.

[fpagliughi]

It would be really helpful if the "connected" callback passed the CONNACK data back to the application (connection present flag, reason code, properties, etc).

This is particularly vital with v5 clients using auto reconnect. With v3, if the session was initially present on the server, you could safely assume the session is still there after a reconnect (or so I've always assumed). But with v5, if the client specifies a session expiry interval, the existing session could disappear before the reconnect completes.

I assume we can't repurpose the unused "cause" pointer, as that might cause some horrific crashes in people's apps. So maybe we can create a new connectedWithData callback, or something like that?

Perhaps another new feature for v1.4?