* 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
* 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