docs: def get_conf_files(filename):
      """
      Return :class:`list` of the all configuration files. *filename* is a
      path of the main configuration file.
  
      ::
  
          >>> get_conf_files('exampleapp.conf')
          ['exampleapp.conf', 'exampleapp.conf.d/10-database.conf']
      """
      if not os.path.isfile(filename):
          raise ValueError("'%s' is not a file" % filename)
      conf_d_path = "%s.d" % filename
      if not os.path.exists(conf_d_path):
          return [filename]
      return [filename] + get_conf_d_files(conf_d_path)