Implement RFC6415

[TCFox]

https://tools.ietf.org/html/rfc6415

[TCFox]

Partially implemented for Mastodon (needs to be committed though):

<?xml version="1.0" encoding="UTF-8"?>
<XRD xmlns="http://docs.oasis-open.org/ns/xri/xrd-1.0">
  <Link rel="lrdd" template="https://mastodon.tc.nz/.well-known/webfinger?resource={uri}"/>
</XRD>