Updated task methods.

Instead of awaiting most tasks, changed to simply returning the tasks.

Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs

@@ -13,8 +13,6 @@ namespace MQTTnet
             if (options == null) throw new ArgumentNullException(nameof(options));
             
             return new MqttClient(options,
-                // The cast to IMqttCommunicationChannel is required... Roslyn is too stupid to
-                // figure out how to cast back to the base type
                 new MqttChannelCommunicationAdapter(options.UseSSL ? new MqttClientSslChannel() : (IMqttCommunicationChannel)new MqttTcpChannel(),
                     new DefaultMqttV311PacketSerializer()));
         }