Support outgoing zone transfers

These can be enabled by adding "transfer out" to the Corefile. Without
it no AXFR is allowed.

For now only AXFR and no IXFR. No TSIG and no ACLs.

middleware/file/file.md

@@ -15,26 +15,15 @@ file dbfile [zones...]
 * `zones` zones it should be authoritative for. If empty the zones from the configuration block
     are used.
 
-If you want to `round robin` A and AAAA responses look at the `loadbalance` middleware.
+If you want to round robin A and AAAA responses look at the `loadbalance` middleware.
 
 ~~~
-file {
-    db <dsds>
-    masters [...masters...]
+file dbfile [zones... ] {
+    transfer in|out
 }
 ~~~
 
-
-
-
-
-* `path` /skydns
-* `endpoint` endpoints...
-* `stubzones`
+* `transfer` enable zone transfers, for now only `transfer out` does something. It enables outgoing
+  zone transfers when defined.
 
 ## Examples
-
-dnssec {
-    file blaat, transparant allow already signed responses
-    ksk bliep.dsdsk
-}