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

Add practical generic detection models containing 676 categories

* fix voc dataset and docs

* add custom datsset demo

* fix README for yolov3

* add NOTE

* fix some docs link error

* rename config_doc

* fix export_model doc link error

* sort out release/0.3 docs

* add new CHANGELOG

* add yolov4 in changelog

* add detailed doc
* add zh_CN doc of pssdet
* fix link

* Update docs
* Update README.md

* add map_fps fig

* Organize and document mobile models

* Clean up trailing whitespaces

* Change bullet type

* Minor wording fixes

* Fix yolo naming

* Add link in repo README.md

* Update README.md
* Update change logs
* Update docs/advanced_tutorials/inference/INFERENCE.md

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* 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).

* 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

* 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

* update code & doc

* Update PaddleDetection README
* Fix some link

This reverts commit 04bfe0a84e7ec27e5c0bdfab76aa779c45fedbe5.

* Add full configs example & refine doc

* refine docs

# Add VGG-SSD on VOC and COCO dataset.
# Add config and model zoo. 
# Refine bbox2out and draw_bbox:
    - Add bbox de-normalize in bbox2out function.
    - Remove bbox de-normalize in draw_bbox.

Add PaddleDetection docs & some model configs

* check gpu for ppdet/yolov3

* add random shape descp in MODEL_ZOO

* refine doc

* not use core

* Add faster_rcnn_x101_vd_64x4d_fpn_1x.yml
* Release faster_rcnn_r101_vd_fpn_1x.tar, faster_rcnn_x101_vd_64x4d_fpn_1x.tar, mask_rcnn_r50_2x.tar

* refine README & use a better visualization for doc

* fix typo in GETTING STARTED