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
Split up the previous changes a bit. This PR only returns the expected
error when the received packet has the wrong EDNS version.
EDNS0 handling in the middleware needs a nicer abstraction, like
ReflectEdns() or something.
