docs: def package_releases(self, package, url_fmt=lambda u: u):
          """List all versions of a package
  
          Along with the version, the caller also receives the file list with all
          the available formats.
          """
          return [{
              'name': package,
              'version': version,
              'urls': [self.get_urlhash(f, url_fmt) for f in files]
          } for version, files in self.storage.get(package, {}).items()]