add gtk3 multi touch event example
http://vbkaisetsu.sky-air.net/wordpress/2012/03/gtk-3-4-%E3%81%AE%E3%82%BF%E3%83%83%E3%83%81%E3%82%A4%E3%83%99%E3%83%B3%E3%83%88%E3%82%92%E8%A9%A6%E3%81%99/