mod_pubsub_mqtt: Support atom_title payload type This commit adds the ability to publish and subscribe with arbitrary payload types. It has a breaking change, which is that topics are now of the form: HOST/TYPE/NODE Currently supported types are utf8_data, json and atom_title.

<tr>
  <th>What is {x} {op} {y}?</th><td>
    <input name="captcha_challenge" type="hidden" value="{challenge}">
    <input name="captcha_reply" pattern="[0-9]+" required type="number">
  </td></tr>