HyperPose 2.2.0

• OpenPifPaf model support (Python Training + C++ Inference);
• Docker container updated to 2.2.0: https://hub.docker.com/repository/docker/tensorlayer/hyperpose
• Add a bunch of new pre-trained models, please check: https://drive.google.com/drive/folders/1w9EjMkrjxOmMw3Rf6fXXkiv_ge7M99jR
• Refactored documents.