code: func RemoveHandlerLevels(h Handler, levels ...Level) {
  	rw.Lock()
  OUTER:
  	for _, lvl := range levels {
  		handlers := logHandlers[lvl]
  		for i, handler := range handlers {
  			if h == handler {
  				n := append(handlers[:i], handlers[i+1:]...)
  				if len(n) == 0 {
  					delete(logHandlers, lvl)
  					continue OUTER
  				}
  				logHandlers[lvl] = n
  				continue OUTER
  			}
  		}
  	}
  	rw.Unlock()
  }
docs: // RemoveHandlerLevels removes the supplied levels, if no more levels exists for the handler
  // it will no longer be registered and need to to added via AddHandler again.