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/errors/setup.go

@@ -0,0 +1,55 @@
+package errors
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("errors", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	handler, err := errorsParse(c)
+	if err != nil {
+		return plugin.Error("errors", err)
+	}
+
+	handler.Log = log.New(os.Stdout, "", 0)
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		handler.Next = next
+		return handler
+	})
+
+	return nil
+}
+
+func errorsParse(c *caddy.Controller) (errorHandler, error) {
+	handler := errorHandler{}
+
+	for c.Next() {
+		args := c.RemainingArgs()
+		switch len(args) {
+		case 0:
+			handler.LogFile = "stdout"
+		case 1:
+			if args[0] != "stdout" {
+				return handler, fmt.Errorf("invalid log file: %s", args[0])
+			}
+			handler.LogFile = args[0]
+		default:
+			return handler, c.ArgErr()
+		}
+	}
+	return handler, nil
+}