Eclipse Mosquitto™ 1.6.4

Broker

• Fix persistent clients being incorrectly expired on Raspberry Pis. Closes #1272.
• Windows: Allow other applications access to the log file when running. Closes #515.
• Fix incoming QoS 2 messages being blocked when `max_inflight_messages` was set to 1. Closes #1332.
• Fix incoming messages not being removed for a client if the topic being published to does not have any subscribers. Closes #1322.

Client library

• Fix MQTT v5 subscription options being incorrectly set for MQTT v3  subscriptions. Closes #1353.
• Make behaviour of `mosquitto_connect_async()` consistent with `mosquitto_connect()` when connecting to a non-existent server. Closes #1345.
• `mosquitto_string_option(mosq, MOSQ_OPT_TLS_KEYFORM, ...)` was incorrectly returning `MOSQ_ERR_INVAL` with valid input. This has been fixed. Closes #1360.
• on_connect callback is now called with the correct v5 reason code if a v5 client connects to a v3.x broker and is sent a CONNACK with the "unacceptable protocol version" connack reason code.
• Fix memory leak when setting v5 properties in mosquitto_connect_v5().
• Fix properties not being sent on QoS>0 PUBLISH messages.

Clients

• mosquitto_pub: fix error codes not being returned when mosquitto_pub exits. Closes #1354.
• All clients: improve error messages when connecting to a v3.x broker when in v5 mode. Closes #1344.

Other

• Various documentation fixes.