* [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.
* resolve conflicts
add heads and config for multilabel tasks
* minor change
* remove evaluating mAP in head
* add baseline config
* add configs
* reserve only one config
* minor change
* fix minor bug
* minor change
* minor change
* add unittests and fix docstrings