* update ssd loss, make it faster test=develop

* update comments, test=develop

* ssd loss, fix bug when no object, text=develop

* add ppyolov2

* fix bugs and modify docs

* modify code and doc according to review

* fix bugs while resolving conflicts

* add pssdet model

* add Distill model

* add distill+prune

* refine ppdet file name

* unify bbox_utils

* fcos infer

* fcos training

* fix stgraph fcosloss

* fcos doc

* fix dy_fcos

* add comment

* train eval deploy fcos

* remove fcos config, add comment

* fix iter_tic
Co-authored-by: Nnemonameless <nemonameless@qq.com>
Co-authored-by: Ngeorgenemo <nifeng@pku.edu.cn>

* add solov2 model

* fix train batch size

* add solov2_r101_vd_fpn_3x

* fix batch size and update modelzoo

* refactor code of solov2

* fix deploy/python

* warning when YOLOv3Loss.batch_size setting

* add batch_size in YOLOv3Loss for backward compatable.

* sync TrainReader.batch to global train_batch_size

* fix deadlink in docs/tutorials/INSTALL_cn.md, slim/README.md and slim/extensions/distill_pruned_model/README.md

* add COCO test-dev eval config and doc

* add PPYOLO
Co-authored-by: Nlongxiang <longxiang@baidu.com>

* add version check

* update version check & python version for cornerpool

* activate scale_x_y

* update cspdarknet pretrained model

* add yolov4

* add iou aware module
* iouaware model zoo
* fix copyright

* fcos initialization

* delete the codes not used

* pre-commit the committed code

* delete the unused function

* modify the capacity in loader from 64 to 16

* exit1 in travis failed

add libra rcnn, including
  * libra loss
  * libra fpn(bfp)
  * libra sampling

* add iou loss to yolov3
* modify the comment and delete redundant yml file
* fix the low speed bug in dropblock module

* add diou nms.
* fix typo in diou nms and soft nms (lod_leval->lod_level).

* Add GIOU loss.
* Add DIOU/CIOU loss.
* Change loss box type in bbox_head.py.
* Remove fuse_elewise_add_act_ops flag in train.py (Error may happen for elem_divbased on the flag).

* split yolov3 loss