Cleanups for Copy()

Docs and slight code formatting issues.

msg.go

@@ -1545,30 +1545,27 @@ func (dns *Msg) Len() int {
 	return l
 }
 
-// Create a deep-copy
+// Copy returns a new *Msg which is a deep-copy of dns.
 func (dns *Msg) Copy() *Msg {
 	r1 := new(Msg)
 	r1.MsgHdr = dns.MsgHdr
 	r1.Compress = dns.Compress
 
 	r1.Question = make([]Question, len(dns.Question))
-	copy(r1.Question, dns.Question) // Question is an immutable value, ok to do a shallow-copy
+	copy(r1.Question, dns.Question) // TODO(miek): Question is an immutable value, ok to do a shallow-copy
 
 	r1.Answer = make([]RR, len(dns.Answer))
 	for i := 0; i < len(dns.Answer); i++ {
 		r1.Answer[i] = dns.Answer[i].copy()
 	}
-
 	r1.Ns = make([]RR, len(dns.Ns))
 	for i := 0; i < len(dns.Ns); i++ {
 		r1.Ns[i] = dns.Ns[i].copy()
 	}
-
 	r1.Extra = make([]RR, len(dns.Extra))
 	for i := 0; i < len(dns.Extra); i++ {
 		r1.Extra[i] = dns.Extra[i].copy()
 	}
-
 	return r1
 }