Add server implementation

MQTTnet.Core/Channel/IMqttCommunicationChannel.cs

@@ -0,0 +1,16 @@
+using System.Threading.Tasks;
+using MQTTnet.Core.Client;
+
+namespace MQTTnet.Core.Channel
+{
+    public interface IMqttCommunicationChannel
+    {
+        Task ConnectAsync(MqttClientOptions options);
+
+        Task DisconnectAsync();
+
+        Task WriteAsync(byte[] buffer);
+
+        Task ReadAsync(byte[] buffer);
+    }
+}