Refactor events.

Frameworks/MQTTnet.NetStandard/Server/IMqttServer.cs

@@ -6,7 +6,8 @@ namespace MQTTnet.Server
 {
     public interface IMqttServer : IApplicationMessageReceiver, IApplicationMessagePublisher
     {
-        event EventHandler<MqttServerStartedEventArgs> Started;
+        event EventHandler Started;
+        event EventHandler Stopped;
 
         event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
         event EventHandler<MqttClientDisconnectedEventArgs> ClientDisconnected;

Frameworks/MQTTnet.NetStandard/Server/MqttServer.cs

@@ -26,7 +26,8 @@ namespace MQTTnet.Server
             _adapters = adapters.ToList();
         }
 
-        public event EventHandler<MqttServerStartedEventArgs> Started;
+        public event EventHandler Started;
+        public event EventHandler Stopped;
 
         public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
         public event EventHandler<MqttClientDisconnectedEventArgs> ClientDisconnected;

Frameworks/MQTTnet.NetStandard/Server/MqttServerEventDispatcher.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Server
+{
+    public class MqttServerEventDispatcher
+    {
+        public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
+        public event EventHandler<MqttClientDisconnectedEventArgs> ClientDisconnected;
+        public event EventHandler<MqttClientSubscribedTopicEventArgs> ClientSubscribedTopic;
+        public event EventHandler<MqttClientUnsubscribedTopicEventArgs> ClientUnsubscribedTopic;
+
+        public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
+    }
+}

Frameworks/MQTTnet.NetStandard/Server/MqttServerStartedEventArgs.cs

@@ -1,8 +0,0 @@
-using System;
-
-namespace MQTTnet.Server
-{
-    public class MqttServerStartedEventArgs : EventArgs
-    {
-    }
-}