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/pprof/pprof.go

@@ -0,0 +1,49 @@
+// Package pprof implement a debug endpoint for getting profiles using the
+// go pprof tooling.
+package pprof
+
+import (
+	"log"
+	"net"
+	"net/http"
+	pp "net/http/pprof"
+)
+
+type handler struct {
+	addr string
+	ln   net.Listener
+	mux  *http.ServeMux
+}
+
+func (h *handler) Startup() error {
+	ln, err := net.Listen("tcp", h.addr)
+	if err != nil {
+		log.Printf("[ERROR] Failed to start pprof handler: %s", err)
+		return err
+	}
+
+	h.ln = ln
+
+	h.mux = http.NewServeMux()
+	h.mux.HandleFunc(path+"/", pp.Index)
+	h.mux.HandleFunc(path+"/cmdline", pp.Cmdline)
+	h.mux.HandleFunc(path+"/profile", pp.Profile)
+	h.mux.HandleFunc(path+"/symbol", pp.Symbol)
+	h.mux.HandleFunc(path+"/trace", pp.Trace)
+
+	go func() {
+		http.Serve(h.ln, h.mux)
+	}()
+	return nil
+}
+
+func (h *handler) Shutdown() error {
+	if h.ln != nil {
+		return h.ln.Close()
+	}
+	return nil
+}
+
+const (
+	path = "/debug/pprof"
+)