Learning how to build gradle enabled android project

01_basic: convert simple eclpise project to gradle enabled project

02_dependency: support library project

03_sign: support apk sign mechanism

04_proguard: use proguard in gradle

05_overlay: build multiple variant

06_as: how to configure gradle correctly with Android Studio (preview)

07_tricks:

• rename and move out built apk files
• support lots of variant and AndroidManifest.xml

08_repo: package library project for faster building