Nameserver entries:
* There's a big FIXME in askIP.
* It has places where TTL should be handled, but isn't yet.

Zone entries:
* They will be nameserver callbacks themself. This ensures that they are not
  destroyed, since the callback is owned by the nameserver and will easy up
  the accessing of internal data structures. Maybe a private inheritance?
* Add ability to time out
* Implement the new interface
* They will create new nameserver entries in constructor.
* Move the logic here from NSAS
* If there are callbacks for this kind of address, do not look into the
  nameserver entries, just add it.
* Even if the TTL is 0, we should accept the first callback.

The NSAS itself:
* If the zone rejects the callback, remove it and call recursively the same
  one. As it will accept at last one, it should not become a loop.
* Do not pass referral info by lookup, it should be fetched on-demand from recursor/cache

Long term:
* Make a mechanism the cache (which does not exist at the time of writing this
  note) will be able to notify the NSAS that something has changed (address,
  new nameserver, etc). Because the cache will have access to the data and
  knows when it changes (it updates its structures), it is the best place. It
  will be caching even data like authority and additional sections. It will
  notify us somehow (we will need to tell it when).
