code: def add_to_item_list(self, item_urls, item_list_url):
          
          item_list_url = str(item_list_url)
          name = self.get_item_list(item_list_url).name()
          return self.add_to_item_list_by_name(item_urls, name)
docs: Instruct the server to add the given items to the specified
          Item List
  
          :type item_urls: List or ItemGroup
          :param item_urls: List of URLs for the items to add,
              or an ItemGroup object
          :type item_list_url: String or ItemList
          :param item_list_url: the URL of the list to which to add the items,
              or an ItemList object
  
          :rtype: String
          :returns: the server success message, if successful
  
          :raises: APIError if the request was not successful