This PR adds the *root* middleware that specifies a path where
all zone file (the *file* middleware is the only consumer now) can
be found. It works the same as in Caddy.
Documentation can be found in the README.md of the middleware.
Fixes#307
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.
Rename: positive -> success
negative -> denial
There is a third (unused category) which is error. Start using these
new in the caching middleware and later in the logging middleware.
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.
