mod_external_services: Factor out public function for converting to XML Along with the previous commit, allows building the XML thing yourself, should you wish to send it yourself or use it in a different context than an iq reply. API change: The 'reply' is removed from the event.

<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>