Eclipse Mosquitto™ 1.6

The main focus of this release is support for the MQTT v5 specification.

Other changes:

Broker features:

• Improved general support for broker generated client ids. Removed libuuid dependency.
• auto_id_prefix now defaults to 'auto-'.
• Add max_keepalive option, to allow a maximum keepalive value to be set for MQTT v5 clients only.
• Add TLS Engine support.
• Add `bind_interface` option which allows a listener to be bound to a specific network interface, in a similar fashion to the `bind_address` option. Linux only.
• Add improved bridge restart interval based on Decorrelated Jitter.
• Add `dhparamfile` option, to allow DH parameters to be loaded for Ephemeral DH support
• Add explicit support for TLS v1.3.
• Drop support for TLS v1.0.
• Add support for Automotive DLT logging.
• Disallow writing to $ topics where appropriate.
• Fix mosquitto_passwd crashing on corrupt password file. Closes #1207.
• Client library features:
• Add mosquitto_subscribe_multiple() for sending subscriptions to multiple topics in one command.
• Add mosquitto_unsubscribe_multiple() for sending unsubscriptions to multiple topics in one command.
• Add TLS Engine support.
• Add explicit support for TLS v1.3.
• Drop support for TLS v1.0.

Client features:

• Add -E to mosquitto_sub, which causes it to exit immediately after having its subscriptions acknowledged. Use with -c to create a durable client session without requiring a message to be received.
• Add --remove-retained to mosquitto_sub, which can be used to clear retained messages on a broker.
• -V now accepts `5, `311`, `31`, as well as `mqttv5` etc.
• Add TLS Engine support.
• Add explicit support for TLS v1.3.
• Drop support for TLS v1.0.

Client fixes:

• mosquitto_pub wouldn't always publish all messages when using `-l` and QoS>0. This has been fixed.