菜鸟教程基础:http://www.runoob.com/svg/svg-tutorial.html
理解SVG坐标系和变换(视窗,viewBox和preserveAspectRatio):http://www.w3cplus.com/html5/svg-coordinate-systems.html
path路径中贝塞尔命令详解:http://www.zhangxinxu.com/wordpress/2014/06/deep-understand-svg-path-bezier-curves-command/
svg中不常见的标签(defs元素、symbol元素和use元素):http://www.htmleaf.com/ziliaoku/qianduanjiaocheng/201506132029.html
svg线性渐变和径向渐变动画:http://www.htmleaf.com/ziliaoku/qianduanjiaocheng/201504141680.html
慕课网视频教程:http://www.imooc.com/view/143