Pass in whole controller now, not just the key

Writing-a-Plugin:-HTTP-Middleware.md

@@ -62,7 +62,7 @@ func setup(c *caddy.Controller) error {
 To chain in your new handler, get the config for the current site from the httpserver package. Then wrap your handler in a middleware function:
  
 ```go
-cfg := httpserver.GetConfig(c.Key)
+cfg := httpserver.GetConfig(c)
 mid := func(next httpserver.Handler) httpserver.Handler {
 	return MyHandler{Next: next}
 }