* Added support for 'dynamic keys' mode, where the router creates a new
      router identity whenever it detects a substantial change in its public
      address (read: SSU IP or port).  This only offers minimal additional
      protection against trivial attackers, but should provide functional
      improvement for people who have periodic IP changes, since their new
      router address would not be shitlisted while their old one would be.
    * Added further infrastructure for restricted route operation, but its use
      is not recommended.