v3.0.9

• [All] Due to a merge issue not all changes are included in 3.0.8. All these changes are now included in this version.
• [Core] Updated all nuget references.
• [Core] Added MqttApplicationMessage.GetUserProperty() convenience method (thanks to @PMExtra).
• [LowLevelMqttClient] Added low level MQTT client in order to provide more flexibility when using the MQTT protocol. This client requires detailed knowledge about the MQTT protocol.
• [Client] Improve connection stability (thanks to @jltjohanlindqvist).
• [Client] Support WithConnectionUri to configure client (thanks to @PMExtra).
• [Client] Support PublishAsync with QoS 1 and QoS 2 from within an ApplicationMessageReceivedHandler (#648, #587, thanks to @PSanetra).
• [Client] Fixed MqttCommunicationTimedOutExceptions, caused by a long running ApplicationMessageReceivedHandler, which blocked MQTT packets from being processed (#829, thanks to @PSanetra).
• [ManagedClient] Added builder class for MqttClientUnsubscribeOptions (thanks to @dominikviererbe).
• [ManagedClient] Added support for persisted sessions (thansk to @PMExtra).
• [ManagedClient] Fixed a memory leak (thanks to @zawodskoj).
• [ManagedClient] Improved internal subscription management (#569, thanks to @cstichlberger).
• [ManagedClient] Refactored log messages (thanks to @cstichlberger).
• [Server] Added support for assigned client IDs (MQTTv5 only) (thanks to @bcrosnier).
• [Server] Added interceptor for unsubscriptions.
• [Server] Removed exceptions when user properties are set with MQTT protocol version 3.1
• [Server] Added custom session items to the client status.
• [Server] Added option to check whether the server is already started properly or not.
• [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1
• [MQTTnet.Server] Added interceptor for unsubscriptions.