itween插件使用

http://wenku.baidu.com/link?url=uhNnd7NuECR2rWhXlnpMeDkxz-DtBl-Yf-iJL3clugNXga6kfEms8NhxIWbP0CthxD_IZw9-j9OfIdmqXiDsn9Z4tj63sNr5QjYZHdQ-k_G

变化曲线：http://robertpenner.com/easing/easing_demo.html