def on_unjoined(target = nil, &block)
      register_event_handler Adhearsion::Event::Unjoined, *guards_for_target(target), &block
    end
def on_unjoined(target = nil, &block)
      register_event_handler Adhearsion::Event::Unjoined, *guards_for_target(target), &block
    end
Registers a callback for when this call is unjoined from another call or a mixer

 @param [Call, String, Hash, nil] target the target to guard on. May be a Call object, a call ID (String, Hash) or a mixer name (Hash)
 @option target [String] call_uri The call ID to guard on
 @option target [String] mixer_name The mixer name to guard on