fix https://github.com/kataras/iris/issues/1713 and add a simple usage example of the 'RemoveHandler'

_examples/routing/remove-handler/main.go

@@ -0,0 +1,29 @@
+package main
+
+import "github.com/kataras/iris/v12"
+
+func main() {
+	app := newApp()
+	app.Listen(":8080")
+}
+
+func newApp() *iris.Application {
+	app := iris.New()
+
+	api := app.Party("/api")
+	api.Use(myMiddleware)
+	users := api.Party("/users")
+	users.Get("/", usersIndex).RemoveHandler(myMiddleware)
+	// OR for all routes under a Party (or Application):
+	// users.RemoveHandler(...)
+
+	return app
+}
+
+func myMiddleware(ctx iris.Context) {
+	ctx.WriteString("Middleware\n")
+}
+
+func usersIndex(ctx iris.Context) {
+	ctx.WriteString("OK")
+}