* [Improve] Speed up data preprocessor.
* Add ClsDataSample serialization override functions.
* Add unit tests
* Modify configs to fit new mixup args.
* Fix `num_classes` of the ImageNet-21k config.
* Update docs.
* [CI] Add Circle CI for mmcls 1.x
* Fix circle-ci config
* Use `torch.cat` instead of `torch.hstack` to compat with PyTorch 1.6
* Compat the behavior of LongTensor in PyTorch 1.6
* Avoid random behavior in the unit test of Lighting
* Fix cuda ci
* Remove github workflow temporarily.