mod_rest/apidemo: Serve yaml with a (non-standard) content-type There's no Standard from what I can tell, found this one somewhere. Serving as text/* might help some clients do something sensible like not treat it as a binary file, which it isn't.

This module helps make BOSH and WebSocket connection endpoints
discoverable via the HTTP method described in
[XEP-0156](https://xmpp.org/extensions/xep-0156.html#http).