* support GN in RetinaHead

* add conv_cfg argument for RetinaHead

* add model upgrading tool and update retinanet model urls

* minor fix for regex strings

Check dataset type by subclass instead of names

Bug fix for freezing BN parameters

Add a tool to process models to be published

* add support for weight standardization

* add ws support for htc heads

* add a config file for 20-23-24e lr schedule

* update readme of weight standardization

Fixed error `TypeError: super(type, obj): obj must be an instance or subtype of type` .

* add HybridTaskCascade

* add configs for other backbones

* add keep_ratio argument for segmap transform

* add readme for HTC

* fix linting errors

* split assign and sampling as in Cascade R-CNN

* remove unused imports

* add a large model

* update htc

* add two stage w/o neck and w/ upperneck

* add rpn r50 c4

* update c4 configs

* fix

* config update

* update config

* minor update

* mask rcnn support c4 train and test

* lr fix

* cascade support upper_neck

* add cascade c4 config

* update config

* update

* update res_layer to new interface

* refactoring

* c4 configs update

* refactoring

* update rpn_c4 config

* rename upper_neck as shared_head

* update

* update configs

* update

* update c4 configs

* update according to commits

* update

* implement _init_dist_slurm()

* add slurm train/test scripts

* fix linting error

* minor fix

Create a new release v0.6.0

remove expand loop in bbox head to speed up

fix dcn to support pytorch-nightly

fix bug in two stage and weighted_binary_cross_entropy_loss

* add cpp sigmoid focal loss

* modify interface

* format cpp code, support, fix pep8 error

* format cpp code as google style

Add an argument in FPN to support building P6 from either C5 or P5

Update evaluation hooks

Add some arguments to DCN ops

* port nms extension from maskrcnn-benchmark

* fix linting error

* fix OHEM with cascade_rcnn

* fix OHEM with cascade_rcnn

* delete space

* delete white space

* delete unused lib

* Delete cascade_rcnn_ohem_r101_fpn_1x.py

* fix unreasonable code

* fix Single quote

* fix code style

* fix code style

* fix file permission

solve deformable_col2im: invalid argument by increasing channel

Instruction for code mofication