* Add markdown lint in pre-commit hook

* add markdown lint

* update Readme of SABL

* update download link

Code Release of ECCV 2020 Spotlight paper for Side-Aware Boundary Localization for More Precise Object Detection (#3603)

* add sabl two stage

* add sabl retina

* ret cfg bug fix

* test bug fix

* minor update

* update

* add r101 two stage

* update

* add cfgs

* add cfgs

* update cfgs

* format

* format

* add readme

* fix isort

* update

* update readme

* add doc string for sabl retina head

* add doc string and rename some functions

* add docstring for bucketing coder

* update docstring

* bucket_num -> num_buckets

* bucket_pw -> bucket_w bucket_ph -> bucket_h

* update label2onehot

* update bucketing bbox coder doc

* update

* typo fix

* bboxes_ -> rescaled_bboxes

* rename some params in sabl head

* init with mmcv.cnn

* update doc

* rename pos->post

* update cfgs

* update test cfg

* update

* add unitest for sabl head

* add unitest for sabl retina

* rename

* minor rename

* minor update

* update docstring

* update

* use F.one_hot

* update docstring

* update test heads

* update ReadMe

* fix