v2.0.0rc2

This release include breaking change. See migrations.md for more details on how to upgrade.

• BREAKING Added callback_api_version. This break ALL users of paho-mqtt Client class.
  See migrations.md for details on how to upgrade.
  tl; dr; add CallbackAPIVersion.VERSION1 to first argument of Client()
• BREAKING Drop support for Python 2.7, Python 3.5 and Python 3.6
  Minimum tested version is Python 3.7
  Python version up to Python 3.12 are tested.
• BREAKING connect_srv changed it signature to take an additional bind_port parameter.
  This is a breaking change, but in previous version connect_srv was broken anyway.
  Closes #493.
• BREAKING Remove some deprecated argument and method:
  • max_packets argument in loop(), loop_write() and loop_forever() is removed
  • force argument in loop_stop() is removed
  • method message_retry_set() is removed
• Possible breaking change: Add properties to access most Client attribute. Closes #764.
  Since this add new properties like logger, if a sub-class defined logger, the two logger
  will conflict.
• Add version 2 of user-callback which allow to access MQTTv5 reason code & properties that were
  missing from on_publish callback. Also it's more consistent in parameter order or between
  MQTTv3 and MQTTv5.
• Add types to Client class, which caused few change which should be compatible.
  Known risk of breaking changes:
  • Use enum for returned error code (like MQTT_ERR_SUCCESS). It use an IntEnum
    which should be a drop-in replacement. Excepted if someone is doing "rc is 0" instead of "rc == 0".
  • reason in on_connect callback when using MQTTv5 is now always a ReasonCode object. It used to possibly be
    an integer with the value 132.
  • MQTTMessage field "dup" and "retain" used to be integer with value 0 and 1. They are now boolean.
• Add support for ALPN protocols on TLS connection. Closes #790 & #648.
• Add on_pre_connect() callback, which is called immediately before a
  connection attempt is made.
• Fix subscribe.simple with MQTTv5. Closes #707.
• Use better name for thread started by loop_start. Closes #617.
• Fix possible bug during disconnection where self._sock is unexpectedly None. Closes #686 & #505.
• Fix loading too weak TLS CA file but setting allowed ciphers before loading CA. Closes #676.
• Allow to manually ack QoS > 0 messages. Closes #753 & #348.
• Improve tests & linters. Modernize build (drop setup.py, use pyproject.toml)
• Fix is_connected property to correctly return False when connection is lost
  and loop_start/loop_forever isn't used. Closes #525.
• Fix wait_for_publish that could hang with QoS == 0 message on reconnection
  or publish during connection. Closes #549.
• Correctly mark connection as broken on SSL error and don't crash loop_forever.
  Closes #750.
• Fix handling of MQTT v5.0 PUBREL messages with remaining length not equal to
  2. Closes #696.
• Raise error on subscribe() when topic is an empty list. Closes #690.
• Raise error on publish.multiple() when msgs is an empty list. Closes #684.
• Don't add port to Host: header for websockets connections when the port if the default port. Closes #666.

Yes it's an rc2 without rc1... that because rc1 failed due to README issue