docs: def set_backend(database):
      """
      Configure used database, so sqlpuzzle can generate queries which are needed.
      For now there is only support of MySQL and PostgreSQL.
      """
      new_backend = BACKENDS.get(database.lower())
      if not new_backend:
          raise Exception('Backend {} is not supported.'.format(database))
      global BACKEND  # pylint: disable=global-statement
      BACKEND = new_backend