Add nuget support

Frameworks/MQTTnet.NetCoreApp/MqttClientFactory.cs

@@ -0,0 +1,17 @@
+using System;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Serializer;
+
+namespace MQTTnet
+{
+    public class MqttClientFactory
+    {
+        public MqttClient CreateMqttClient(MqttClientOptions options)
+        {
+            if (options == null) throw new ArgumentNullException(nameof(options));
+
+            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+        }
+    }
+}