* add ema hook
* add ema hook resume
* add ema hook test
* fix typo
* fix according to comment
* delete logger
* fix according to comment
* fix unitest
* fix typo
* fix according to comment
* change to resume_from
* typo
* fix isort
* fix: remove all module wrapper when saving checkpoint
* refactor: move position of if
* docs: add docstring
* refactor: add _save_to_state_dict from official torch
* docs: modify docstring of _save_to_state_dict
* docs: modify docstring
* feat: add unittest
* feat: add DataParallel to unittest
* fix: a bug when model has batchnorm
* docs: update docstring
* feat: support for os.environ port for slurm training
* fix: port data type
* feat: add flawed unittest
* feat: add flawed unittest
* docs: add comments
* fix: unittest
* fix: unittest
* feat: add CosineRestartLrUpdaterHook
* style: rename period to periods
* fix: bug in period 0
* feat: rename eta_min to min_lr and add min_lr_ratio
* docs: fix docstring of restart lr updater
* refactor: use annealing_cos
* docs: add docstring to annealing_cos
* feat: cosine restart lr update hook
* refactor: modify code order for unittest
* add a BaseRunner and rename Runner to EpochBasedRunner
* fix the train/val step
* bug fix
* update unit tests
* fix unit tests
* raise an error if both batch_processor and train_step are set
* add a unit test