Download data for a given Kaggle competition.

def download_kaggle_data(self, competition_name):
    """Download data for a given Kaggle competition."""
    with self._downloader.tqdm():
      kaggle_downloader = self._downloader.kaggle_downloader(competition_name)
      urls = kaggle_downloader.competition_urls
      files = kaggle_downloader.competition_files
      return _map_promise(self._download,
                          dict((f, u) for (f, u) in zip(files, urls)))