package by feature or layer.(Android 客户端代码如何划分包名）
参考文档：
package by feather, not layer
http://www.javapractices.com/topic/TopicAction.do?Id=205
其他:
http://android.jobbole.com/82480/
https://www.jianshu.com/p/45c1675bec69
https://www.cnblogs.com/bhm666/p/6609558.html
