[Docs] Make API of docs clearer (#469)

.gitignore

docs/en/_static/css/readthedocs.css

docs/en/_templates/classtemplate.rst

docs/en/api.rst

docs/en/api/config.rst

docs/en/api/dataset.rst

docs/en/api/device.rst

docs/en/api/dist.rst

docs/en/api/evaluator.rst

docs/en/api/fileio.rst

docs/en/api/hooks.rst

docs/en/api/hub.rst

docs/en/api/logging.rst

docs/en/api/model.rst

docs/en/api/optim.rst

docs/en/api/registry.rst

docs/en/api/runner.rst

docs/en/api/structures.rst

docs/en/api/utils.dl_utils.rst

docs/en/api/utils.rst