v0.3.0

• BC: a host that does not resolve throws the new ResolutionFailed
  (NetworkExceptionInterface) instead of RequestRefused with
  Refusal::Unresolvable (the case is removed). The system resolver cannot
  tell NXDOMAIN from SERVFAIL or a timeout, so the failure may be temporary
  and callers that retry network failures now retry it (found by the
  cska-one pilot: link previews of a briefly unresolvable host were parked
  for a week as permanent).