title: Define a jsonable type using mypy / PEP-526
body: <p>Values that can be converted to a JSON string via <code>json.dumps</code> are:</p>
  <ul>
  <li>Scalars: Numbers and strings</li>
  <li>Containers: Mapping and Iterable</li>
  </ul>
  <p><code>Union[str, int, float, Mapping, Iterable]</code></p>
  <p>Do you have a better suggestion?</p>