* Support ResNeSt backbone

* fixed avg_down

* add docstring and test

* update table

* update docs and tests

* fixed test

* rename

* refactor splits

* Generalized OHEM

* remove config

* update docstring

* fixed sort prob

* fixed valid_mask

* add test tutorial

* remote torch/torchvision from requirements

* update getting started

* rename drop_out_ratio -> dropout_ratio