教程：
http://www.cnblogs.com/davenkin/p/gradle-learning-1.html
http://blog.csdn.net/a38017032/article/details/61414772
http://www.jianshu.com/p/9df3c3b6067a
gradle自定义配置：
http://blog.csdn.net/nwsuafer/article/details/42006625
http://blog.csdn.net/killfunst/article/details/44996933
http://blog.csdn.net/gxl3999/article/details/44282469