Little change of session API + Update examples

Former-commit-id: e8c58b186acf1c8932af6e886dae7035f4d581c1

_examples/sessions/standalone/main.go

@@ -69,6 +69,11 @@ func main() {
 		sess.Start(ctx).Clear()
 	})
 
+	app.Get("/update", func(ctx context.Context) {
+		// updates expire date
+		sess.ShiftExpiraton(ctx)
+	})
+
 	app.Get("/destroy", func(ctx context.Context) {
 
 		//destroy, removes the entire session data and cookie