A health middleware

Start http handler on port 8080 and return OK. Also add some

documentation fixes for the prometheus middleware.

core/setup/health.go

@@ -0,0 +1,33 @@
+package setup
+
+import (
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/health"
+)
+
+func Health(c *Controller) (middleware.Middleware, error) {
+	addr, err := parseHealth(c)
+	if err != nil {
+		return nil, err
+	}
+
+	h := health.Health{Addr: addr}
+	c.Startup = append(c.Startup, h.ListenAndServe)
+	return nil, nil
+}
+
+func parseHealth(c *Controller) (string, error) {
+	addr := ""
+	for c.Next() {
+		args := c.RemainingArgs()
+
+		switch len(args) {
+		case 0:
+		case 1:
+			addr = args[0]
+		default:
+			return "", c.ArgErr()
+		}
+	}
+	return addr, nil
+}