• Fix retain msg server race condition preventing some messages from being
  persisted and replicated to other nodes in the cluster (#507).
• Log when a client is disconnected and multiple sessions are not allowed.
• Fix tracer mountpoint parameter bug.
• Make it possible to add/inject HTTP API keys.
• Add Erlang VM memory usage stats to the exposed metrics.
• Fix bug with max_message_size and message_size_limit only one of these
  should exist and message_size_limit has now been deprecated and no longer
  has any effect. max_message_size should be used instead.
• Fix bug in vmq_diversity where the MongoDB client pool would not reconnect
  after a MongDB restart (#475).
• Fix bug in vmq_diversity where the PostgreSQL client pool would not reconnect
  after a PostgreSQL restart (same as #475).