Filter results of Webfinger request per the rel parameter

[evanp]

When a rel parameter is provided, maybe we should scrub the results of anything that doesn't match the rel parameter?

Some servers will ignore the rel parameter; others will return incorrect data. Others that don't support the /.well-known/webfinger endpoint will end up with the full JRD document.

We could optionally do this filtering on the client side, with maybe a {nofilter: true} flag for those who want to rawdog it?