https://kotlin.link/
https://github.com/huanglizhuo/kotlin-in-chinese
http://kotlinlang.org/docs/tutorials/kotlin-android.html
https://juejin.im/post/591dd9f544d904006c9fbb96
// 谷歌官方实例文件
https://developer.android.com/samples/index.html?language=kotlin
start Kotlin
https://developer.android.com/kotlin/get-started.html
https://android-developers.googleblog.com/2017/05/android-announces-support-for-kotlin.html