Cleanup: put middleware helper functions in pkgs (#245)

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

request/request_test.go

@@ -0,0 +1,55 @@
+package request
+
+import (
+	"testing"
+
+	"github.com/miekg/coredns/middleware/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestRequestDo(t *testing.T) {
+	st := testRequest()
+
+	st.Do()
+	if st.do == 0 {
+		t.Fatalf("Expected st.do to be set")
+	}
+}
+
+func TestRequestRemote(t *testing.T) {
+	st := testRequest()
+	if st.IP() != "10.240.0.1" {
+		t.Fatalf("Wrong IP from request")
+	}
+	p := st.Port()
+	if p == "" {
+		t.Fatalf("Failed to get Port from request")
+	}
+	if p != "40212" {
+		t.Fatalf("Wrong port from request")
+	}
+}
+
+func BenchmarkRequestDo(b *testing.B) {
+	st := testRequest()
+
+	for i := 0; i < b.N; i++ {
+		st.Do()
+	}
+}
+
+func BenchmarkRequestSize(b *testing.B) {
+	st := testRequest()
+
+	for i := 0; i < b.N; i++ {
+		st.Size()
+	}
+}
+
+func testRequest() Request {
+	m := new(dns.Msg)
+	m.SetQuestion("example.com.", dns.TypeA)
+	m.SetEdns0(4097, true)
+	return Request{W: &test.ResponseWriter{}, Req: m}
+}