Run golint and go vet (#276)

Cleanup the errors and removed deadcode along the way. The leaves
some error laying around, mostly about commenting exported identifier.
We should look hard if those really are needed.

middleware/pkg/rcode/rcode.go

@@ -6,6 +6,8 @@ import (
 	"github.com/miekg/dns"
 )
 
+// ToString convert the rcode to the offical DNS string, or to "RCODE"+value if the RCODE
+// value is unknown.
 func ToString(rcode int) string {
 	if str, ok := dns.RcodeToString[rcode]; ok {
 		return str