Panic immediately on invalid conntype in lookup
Remove JRD host-meta lookup.
I misread the spec, the XML version is required and the JSON version is
optional, you don't get to pick between the two. This will be clarified
in version 1.1.2 of XEP-0156: https://github.com/xsf/xeps/pull/198
internal: Unmarshal JSON or XML host-meta files
internal: Add host-meta XRD struct