v3.0.0-alpha.1

• Replace paho-mqtt dependency with mqtt5
• Drop support for MQTTv3.1 and MQTTv3.1.1
• All Client parameters are now keyword-only
• Messages are now mqtt5.PublishPacket instances instead of aiomqtt.Message
• publish payload is now a positional bytes argument instead of keyword payload=
• client.messages is now client.messages() (method call)
• message.mid renamed to message.packet_id
• message.properties replaced by individual attributes (e.g. message.content_type, message.user_properties)
• Manual acknowledgment of QoS=1 and QoS=2 messages (no longer automatic)
• packet_id parameter for QoS>0 publishes, enabling retries via client.packet_ids
• Built-in reconnection with exponential backoff via reconnect=True
• client.connected() and client.disconnected() awaitables for connection state
• Flow control via receive_max
• Unix domain socket support via unix_socket parameter
• ssl_context replaces tls_context, tls_params, and tls_insecure
• qos subscription parameter renamed to max_qos
• ConnectError, ProtocolError, and NegativeAckError replace MqttError
• Remove protocol, transport, proxy, socket_options, timeout, queue_type, max_queued_incoming_messages, max_queued_outgoing_messages parameters
• Remove message.topic.matches() (see guides for routing with regular expressions)