Wind0ws Rxbus2 Versions Save

1. Modify RxBus annotation method logic, will throw exceptions if method invoke failed. Now support private annotation method.
2. Refactor method.
3. Update demo.
4. Add javadoc

1. Fix RxSubscribe annotation EventThread bug.
2. Remove unnecessary method.
3. Update README.

• Update gradle and rxjava version.
• Add proguard rules on demo.
• Refactor some method and remove some unnecessary method.

Release first version of rxbus2. Support annotation, sticky event,PublishBus/BehaviorBus/ReplayBus.