(PECL ev >= 0.2.0)
EvLoop::signal — Creates EvSignal watcher object associated with the current event loop instance
$signum
   ,$callback
   ,$data
     = null
   ,$priority
     = 0
   Creates EvSignal watcher object associated with the current event loop instance
All parameters have the same meaning as for EvSignal::__construct()
Returns EvSignal object on success