v1.0.0 released

• Refactor the code for future update and maintenance.
• Add Federated Learning with MPC, which supports horizontal, vertical and transfer Federated Learning.
• Add load & transfer program from normal model to PaddleFL, supporting more models and scenarios.
• Add document and instructions for all demos to make them easy to follow.
• Provide official docker image, pull and use PaddleFL easily.