Startup notification (#250)

Stop the caddy message and start our own init notifications.
Log the version of CoreDNS when starting up.
Fix all middleware's setup functions so that return the error prefixed
with *which* middleware was failing; leads to better debuggable errors
when starting up.

middleware/secondary/setup.go

@@ -18,7 +18,7 @@ func init() {
 func setup(c *caddy.Controller) error {
 	zones, err := secondaryParse(c)
 	if err != nil {
-		return err
+		return middleware.Error("secondary", err)
 	}
 
 	// Add startup functions to retrieve the zone and keep it up to date.