some of the global config values are reference type, e.g., objects, lists or
dicts, if the created module instances modify those values (see FPN and
spatial_scale), global config will reflect these changes, and instances of the
same class created later will inherit the changed values

* refine bbox_normalize in infer.py

* add is_bbox_normalize

* rename _forward to build

* check callable

* 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

* add save_inference_model in infer.py

* format code

* add comment

* add save_inference_model doc

* refine doc

* Fix some docs
* Unify COCO and VOC
* Change PASCAL to Pascal
* Unify dataset/coco

* improve quality of images

* update url for install doc

* refine README & use a better visualization for doc

* fix typo in GETTING STARTED

* Update README.md and GETTING_STARTED.md for PaddleDetection.

* fix model zoo doc

* update yolov3/ssd bbox AP

* refine MODEL ZOO

* fix AP

* add size 416 320

* fix link

* fix format

* fix align

* update darknet53 pretrain link

* update weights path

* Rename object_detection to PaddleDetection
* Small fix for doc