Provide an XML export of the pilot weight data

[eallrich]

In addition to the JSON export, provide the same data (and in a similar format) in XML. The intent is to make consumption of the exports easier for other systems which have better support for XML parsing vs. JSON parsing.

Possible schema:

<pilotweights>
  <version>1</version>
  <updated>2015-10-17T23:29:45</updated>
  <pilot>
    <lastname>Pilot</lastname>
    <firstname>Kim</firstname>
    <weight>100</weight>
  </pilot>
  ...
</pilotweights>