tor-parallel-relay-conn/changes/decouple_control_events

  o Code simplification and refactoring:
    - When generating an event to send to the controller, we no longer
      put the event over the network immediately.  Instead, we queue
      these events, and use a Libevent callback to deliver them.
      This change simplifies Tor's callgraph by reducing the number
      of functions from which all other Tor functions are reachable.
      Closes ticket 16695.