* update YOLOv3_ENHANCEMENT.md
* update IoUloss and DropBlock configs for YOLOv3 related configs

* add slim MODEL_ZOO to docs

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* add gcnet model : https://arxiv.org/abs/1904.11492

* refine code & doc for cpp_infer

* add cython for pycocotools install

* load inference

* add doc

* add config file for tensorrt_infer

* add padding for rcnn preprocess

* refine code & doc

`--minimal` is option for `generate` and should be positioned after it

* 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

* add res2net model

* modify yml files

* add res2net model zoo

* add hrnet model

* modify model zoo

* minor fix readme

* update readme in dirs

* minor fix softnms bug

* refine model zoo

* modify yml files

* modify pretrain names

* Polish Reader to simplify preprocessing logic.
#  sample_transforms-> make batch -> batch_transforms in Reader.
* Clean some code
* Imporve yolov3_r50vd_dcn_obj365_pretrained_coco 41.4 to 41.8.
* Update all configs.

* Add cascade_rcnn_cls_aware_r200_vd_fpn_dcnv2_nonlocal_softnms model on oidv5 and obj365.
* Add obj365 config annotation
* Update docs.

* move path to PaddleDetection repo in docs

* refine README

* change fluid.layers.data to fluid.data

* fix export_model doc

* add softnms, nonlocal, resnet200_vd_backbone
* add CBNet
* update model zoo

* update code & doc

* change voc_loader

* add x2coco.py

* Update DATA.md

* Update DATA_cn.md

* add export_model doc

* add CACascadeRCNN doc
* add pretrain model download link

* Update PaddleDetection README
* Fix some link

* Update PaddleDetection/README_cn.md
* Follow comments
* Small update

* Add inference benchmark
* Adjustment order
* Update some descriptions

* refine doc for transfer learning

* add face doc
* update face detection readme and add demo jpg

* refine download sh to py

* update QUICK_STARTED

* Error out if fp16 is enabled and affine channel is used

* Add more documentation on mixed precision training