Move all (almost all) Go files in middleware into their
own packages. This makes for better naming and discoverability.
Lot of changes elsewhere to make this change.
The middleware.State was renamed to request.Request which is better,
but still does not cover all use-cases. It was also moved out middleware
because it is used by `dnsserver` as well.
A pkg/dnsutil packages was added for shared, handy, dns util functions.
All normalize functions are now put in normalize.go
Return a delegation when seeing one while traversing the tree in
search of an answer.
Put the SOA and NS record in the zone.Apex as these are to be handled
somewhat special.
Lowercase record on insert to make compares easier. This lowercases
all RR that have domain names in their rdata as well.
