• Fix issue with PUBREL frames retried after client reconnects (#762).
• Refactor and cleanup retry mechanism.
• 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).