code: func listKeys(db keyval.ProtoBroker) {
  	resp, err := db.ListKeys(phonebook.EtcdPath())
  	if err != nil {
  		log.Fatal(err)
  	}
  
  	fmt.Println("list keys:")
  	for {
  		key, _, stop := resp.GetNext()
  		if stop {
  			break
  		}
  
  		fmt.Printf("- %s\n", key)
  
  	}
  }
docs: // listKeys lists keys