Add extension methods that provide a simpler api for IMqttClient and IManagedMqttClient connect/disconnect when the handlers do not need async/await

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientExtensions.cs

@@ -24,6 +24,18 @@ namespace MQTTnet.Extensions.ManagedClient
             return client;
         }
 
+        public static IManagedMqttClient UseConnectedHandler(this IManagedMqttClient client, Action<MqttClientConnectedEventArgs> handler)
+        {
+            if (handler == null)
+            {
+                client.ConnectedHandler = null;
+                return client;
+            }
+
+            client.ConnectedHandler = new MqttClientConnectedHandlerDelegate(handler);
+            return client;
+        }
+
         public static IManagedMqttClient UseDisconnectedHandler(this IManagedMqttClient client, Func<MqttClientDisconnectedEventArgs, Task> handler)
         {
             if (handler == null)
@@ -36,6 +48,18 @@ namespace MQTTnet.Extensions.ManagedClient
             return client;
         }
 
+        public static IManagedMqttClient UseDisconnectedHandler(this IManagedMqttClient client, Action<MqttClientDisconnectedEventArgs> handler)
+        {
+            if (handler == null)
+            {
+                client.DisconnectedHandler = null;
+                return client;
+            }
+
+            client.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(handler);
+            return client;
+        }
+
         public static IManagedMqttClient UseReceivedApplicationMessageHandler(this IManagedMqttClient client, Func<MqttApplicationMessageHandlerContext, Task> handler)
         {
             if (handler == null)

Source/MQTTnet/Client/MqttClientExtensions.cs

@@ -27,6 +27,18 @@ namespace MQTTnet.Client
             return client;
         }
 
+        public static IMqttClient UseConnectedHandler(this IMqttClient client, Action<MqttClientConnectedEventArgs> handler)
+        {
+            if (handler == null)
+            {
+                client.ConnectedHandler = null;
+                return client;
+            }
+
+            client.ConnectedHandler = new MqttClientConnectedHandlerDelegate(handler);
+            return client;
+        }
+
         public static IMqttClient UseDisconnectedHandler(this IMqttClient client, Func<MqttClientDisconnectedEventArgs, Task> handler)
         {
             if (handler == null)
@@ -39,6 +51,18 @@ namespace MQTTnet.Client
             return client;
         }
 
+        public static IMqttClient UseDisconnectedHandler(this IMqttClient client, Action<MqttClientDisconnectedEventArgs> handler)
+        {
+            if (handler == null)
+            {
+                client.DisconnectedHandler = null;
+                return client;
+            }
+
+            client.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(handler);
+            return client;
+        }
+
         public static IMqttClient UseReceivedApplicationMessageHandler(this IMqttClient client, Func<MqttApplicationMessageHandlerContext, Task> handler)
         {
             if (handler == null)