* add densenet, squeezenet, darknet, resnext, resnext101_wsl pretrained models

* add deformable models
* fix dcn v2
* fix log_iter

Fix typos in DAM readme

* using new load api

* fix transformer crashed when dropout seed get None

* fix cn docs

* fix ssd eval_coco_map bug

* fix easy problem

* update GETTING_STARTED.md

Add PaddleDetection docs & some model configs

* add voc_eval and yolo_darknet_voc

* add yolov3_darknet_voc in MODEL_ZOO

* fix default im_size

* fix MODEL_ZOO note

* fix is_bbox_normalized

* extract map to map_utils.py

* update yolov3_dorknet_voc mixup

* add yolov3_r34_voc

* add yolov3_mobilenet_v1_voc

* fix drop empty in VAL mode

* use cfg.num_classes

* assert metric valid

* enable difficulty can be None

* add comment for bbox_eval

* num_classes in retinanet

* Fix ResizeImage and data transform for SSD
* Fix code style

option should not be overridden by subsequent options of the same module.

* fix gpu detection issue on windows
1. use the fluid.core.get_cuda_device_count() to decide the GPU number
2. ignore the path missing issue

* add log iter argument

* ppdet log time smooth

* ppdet log eta

* refine gan