rtfc 0.7.0

Phase 3, beyond the office: contacts on a VPN or Tailscale.

Added

• rtfc hints (and /rtfc:hints) shows the addresses your invites tell people to
  connect to, and add, remove and auto change them: add a VPN address or a Tailscale
  name, drop one nobody can reach, or go back to auto-detection. Changes apply to the running
  daemon at once and go into new invites.
• Contacts refresh each other's addresses whenever they talk. Every session's hello now
  carries the sender's hints, so a contact who moves to a VPN is reachable the next time
  either side sends, with no new invite.
• rtfc contacts shows each device's hints.

Changed

• All of a device's addresses are tried at once, a quarter second apart, and the first to
  answer wins. They used to be tried one after another with a three-second timeout each, so a
  contact's office address timed out before their VPN address was tried, and the "who's home"
  check called them away.
• Auto-detected hints no longer include link-local addresses (169.254.x.x, one per idle
  adapter on Windows) or loopback, each of which cost contacts a connection attempt.

A 0.6.x daemon ignores the hints in a hello and keeps working; the wire protocol stays at
version 1.