• Fix issue in the bridge preventing it from reconnecting after a connection
  timeout (#726).
• Fix issue with self referential cluster leaves and cluster readiness probing
  in general (#717).
• Add preparations for MQTTv5:
  • Make it possible to extend the cluster internal message format when adding
    new features while ensuring back- and forwards compatibility.
  • Refactor the leveldb message store code to support versioned indexes as well
    as messages.
  • Refactor the retained message store to support versions.
  • Add support for subscriber data with subscription options.
• Fix issue when validating a shared subscription topic (#756).
• Fix issue with retried PUBREC frames (#750).
• Make it possible to suppress the Last Will and Testament message if an
  existing session already exists for the connecting client. This is
  configurable via the hidden setting suppress_lwt_on_session_takeover in the
  VerneMQ configuration file. The default is off.
• Fix issue with PUBREL frames retried after client reconnects (#762).
• Refactor and cleanup retry mechanism.
• Warn about deprecated setting message_size_limit only when it has been defined.
• Change build script so nightly packages will have names on the form
  vernemq_1.4.0-10-gde1b1f5-1_amd64.deb, where de1b1f5 refers to the commit
  hash from which the package was built and 10 is the number of commits since
  the latest tag. This makes it much easier to reason about nightly builds and
  the features they contain.
• Refactor and generalize the metrics systems to allow labelling metrics coming
  from different sources in order to differentiate them in the various exporters
  and the command line. Labels are added to the Prometheus exporter by
  default. To enable generating additional metrics from the labels in the
  graphite exporter the hidden setting graphite_include_labels has to be set
  to on in the vernemq.conf file. Labels are not exposed in the $SYS
  metrics.
• Ensure the vmq_bridge is properly restarted after a crash (#785).
• Fix issue where not calling http.body(ref) in a Lua script would not return
  the underlyning HTTP connection to the connection pool. This now happens
  automatically, irregardless of the user calling http.body(ref) or not
  (#588).