About client lifecycle

[wwhai]

Description

Should add an event interface which named OnConnected, Because that's only have OnConnect , But it seems only suit for todo something BEFORE connect，when we open Auth plugin，'OnConnected' maybe not trigger if auth failure。

Such bellow

type Events struct {
	OnProcessMessage // published message receieved before evaluation.
	OnMessage          // published message receieved.
	OnError                // server error.
	OnConnect           // client ready connect.
        OnConnected        // client connected.
	OnDisconnect       // client disconnected.
	OnSubscribe        // topic subscription created.
	OnUnsubscribe    // topic subscription removed.
}

[wind-c]

Authentication failure is also an error and can be detected by events#OnError.