安装及基本用法由此连接http://www.cnblogs.com/jys509/p/4839803.html
提示：
(1)在最后一步，pod install已经不能使用，应该用pod install --verbose --no-repo-update就可以了
（2）有时候会出现这种警告：
Your Podfile has had smart quotes sanitised. To avoid issues in the future, you should not use TextEdit for editing it. If you are not using TextEdit, you should turn off smart quotes in your editor of choice
解决办法是把每个引入的库都用~>标明版本号。
