middleware/httpproxy: Add (#439)

This PR adds a middleware that talks to dns.google.com over HTTPS,
meaning all your DNS traffic is encrypted when traversing your ISP and
the internet.

The `dns.google.com` address is re-resolved every 30 seconds.

core/coredns.go

@@ -15,6 +15,7 @@ import (
 	_ "github.com/miekg/coredns/middleware/etcd"
 	_ "github.com/miekg/coredns/middleware/file"
 	_ "github.com/miekg/coredns/middleware/health"
+	_ "github.com/miekg/coredns/middleware/httpproxy"
 	_ "github.com/miekg/coredns/middleware/kubernetes"
 	_ "github.com/miekg/coredns/middleware/loadbalance"
 	_ "github.com/miekg/coredns/middleware/log"

core/dnsserver/directives.go

@@ -94,5 +94,6 @@ var directives = []string{
 	"etcd",
 	"kubernetes",
 	"proxy",
+	"httpproxy",
 	"whoami",
 }