Created by: lcy-seso

• Currently, how each demos run in models repo varies from demo to demo. Except for some very complicated demo, for example, DS2, it is better to unify the organization of the code.
• At least the following work is required:
  • create command line interfaces for each example.
  • add docstring for each important function, and unify the style of docstring. Keep the style be consistent with PaddlePaddle main repo.