* update reader in dygraph

* update dataloader some detail

* fix num_classes with background

* rename GridMaskOp to GridMask in ppdet/data/transform/operator.py to avoid conflict

* fix bugs in operator and batch_operator and check_version

* modify name in GridMask

* add comma according to review

* split config into models, optimizers, dataset, readers，runtime

* modify operators and batch_operators in data preprocess

* import BboxError and ImageError in operators

* modify code according to review

* modify some bugs

* add Gt2Solov2TargetOp in batch_operators

* modify code according to review

* migrate detection ops from Paddle to PaddleDetection

* add unittest for detection ops

* update api & unittest

* add copyright & api name to migrate

* refactor dygraph & add mask rcnn fpn

* fix initialization & minor update

* refine architecture of mask_rcnn

sync reader from static ppdet

add train&eval 
add reader padding 
add new config 

* filter illegal data

* update warning message

* optimize python path

* add yolov4

* Make logger less noisy

* Fix indent

* code for cornernet

* add doc

* refine custom op

* refine code from review comments

* refine doc

* update doc

* update code

* add cornernet_squeeze_mixup_cosine config

* update code

* update code

* 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

* add mask operations in RandomExpand and RandomCrop

* remove all [] in cropped polys

* is_poly -> _is_poly()

* change the judgment on whether there are polygons

* abstract is_poly to op_helper.py

* add is_mask_expand and is_mask_crop in RandomExpand and RamdomCrop

* add mask operations in RandomExpand and RandomCrop

* remove all [] in cropped polys

* is_poly -> _is_poly()

* change the judgment on whether there are polygons

* abstract is_poly to op_helper.py

* add devices_num on reader

* refine capacity value

* refine bufsize

* add autoaugment, which is validated on faster-rcnn

* enable data unittest

* exit1 in travis failed

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* refine cocoapi import

* fix infer when anno_path is None

* split yolov3 loss

* 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.

* Update x2coco.py to fix the cityscape bug when split dataset  

Fix hang bug in parallel_map.py when multiprocessing mode used and some consumer exit abnormally (#106)

* Update GETTING_STARTED_cn.md
* Update x2coco.py