Enums vs IntDef in Android
- http://tools.android.com/tech-docs/support-annotations
- https://developer.android.com/intl/es/tools/debugging/annotations.html#enum-annotations
- https://www.reddit.com/r/androiddev/comments/33hct2/intdef_new_enums_for_android_development/
- https://noobcoderblog.wordpress.com/2015/04/12/java-enum-and-android-intdefstringdef-annotation/
- https://www.youtube.com/watch?v=Hzs6OBcvNQE