Fix transferring the zone from a master and the matching of notifies
to source and dst IP addresses.
Add `upstream` keyword as well, because it is needed for the same
reasons as in the *file* middlware.
Add some dire warning about upstream in the readme of both middlewares.
Out of band testing, hidden by net build tag was added. Integration
testing still needs to be setup.
This still needs cleanup, but this is a first pass the cleans some
cruft and documents our style (in middleware.md) and makes all the
docs match that style.
Allow specifying a primary server and retrieve the zone's content.
Add tests and an Expired bool to zone struct, to stop server zones
that are expired. The zone is retrieved on Startup, no updates of
changed content are done. We also don't respond to notifies yet.
