Returns the completion percentage (0 to 100) for a given device
            and folder.

            Args:
                device (str): The Syncthing device the folder is syncing to.
                folder (str): The folder that is being synced.

            Returs:
                int

def completion(self, device, folder):
        """ Returns the completion percentage (0 to 100) for a given device
            and folder.

            Args:
                device (str): The Syncthing device the folder is syncing to.
                folder (str): The folder that is being synced.

            Returs:
                int
        """
        return self.get(
            'completion',
            params={'folder': folder, 'device': device}
        ).get('completion', None)