Fix some stability issues and finetune documents on v0.3.0

Major Features

Add an EDL application: distributed distillation

• Support elastic training with inference type services during training, such as knowledge distillation
• Inference type services are automatically registered through service discovery in EDL
• Knowledge distillation examples in computer vision and natural language processing

And we will release a new version later that automatically adjusts teachers based on traffic.

Release log

Major Features

1. Add EDL launcher to Manage Trainers on one Container.
2. Add JobServer and JobClient to simulate a cluster environment and add the tutorial to test with them.
3. Add EDL version of Resnet model and it can do EDL training by checkpoint every epoch.

this is the first release for EDL, just initial release.