Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/pkg/replacer/replacer_test.go

@@ -0,0 +1,61 @@
+package replacer
+
+import (
+	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/dnsrecorder"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestNewReplacer(t *testing.T) {
+	w := dnsrecorder.New(&test.ResponseWriter{})
+
+	r := new(dns.Msg)
+	r.SetQuestion("example.org.", dns.TypeHINFO)
+	r.MsgHdr.AuthenticatedData = true
+
+	replaceValues := New(r, w, "")
+
+	switch v := replaceValues.(type) {
+	case replacer:
+
+		if v.replacements["{type}"] != "HINFO" {
+			t.Errorf("Expected type to be HINFO, got %q", v.replacements["{type}"])
+		}
+		if v.replacements["{name}"] != "example.org." {
+			t.Errorf("Expected request name to be example.org., got %q", v.replacements["{name}"])
+		}
+		if v.replacements["{size}"] != "29" { // size of request
+			t.Errorf("Expected size to be 29, got %q", v.replacements["{size}"])
+		}
+
+	default:
+		t.Fatal("Return Value from New Replacer expected pass type assertion into a replacer type\n")
+	}
+}
+
+func TestSet(t *testing.T) {
+	w := dnsrecorder.New(&test.ResponseWriter{})
+
+	r := new(dns.Msg)
+	r.SetQuestion("example.org.", dns.TypeHINFO)
+	r.MsgHdr.AuthenticatedData = true
+
+	repl := New(r, w, "")
+
+	repl.Set("name", "coredns.io.")
+	repl.Set("type", "A")
+	repl.Set("size", "20")
+
+	if repl.Replace("This name is {name}") != "This name is coredns.io." {
+		t.Error("Expected name replacement failed")
+	}
+	if repl.Replace("This type is {type}") != "This type is A" {
+		t.Error("Expected type replacement failed")
+	}
+	if repl.Replace("The request size is {size}") != "The request size is 20" {
+		t.Error("Expected size replacement failed")
+	}
+}