requestanimationframe 时间间隔 实测 chorome47 下约 16,17ms
https://www.npmjs.com/package/bezier-easing
http://haiyang.me/easing/animating_with_easing_functions_in_javascript.htm
http://haiyang.me/easing/svg_path.htm
http://haiyang.me/easing/Easings.html
http://haiyang.me/easing/cubic.html
http://mojs.io/tutorials/easing/path-easing/
http://haiyang.me/easing/tween05.html