* add faster_rcnn_r50_fpn and faster_rcnn_r50

* update TestReader in dygraph

* if gt_ploy is empty, continue

* fix typo

* judge gt_ploy is empty or not

* fix judge condition

* fix gt_ploy judge

* add INSTALL_cn.md, GETTING_STARTED_cn.md, and MODEL_ZOO_cn.md for dygraph

* add Custom_DataSet.md and PrepareDataSet.md for dygraph

* add Custom_DataSet.md later

* update document

* update resnet50 pretrained weights link

* fix typo

* add set dataset path in doc, test=document_fix

* refine resume process and modify code to support eval while batch_size is larger than 1

* modify code according to review

* replace RandomDistortOp with ColorDistort

* modify RandomDistortOp

* remove hsv_format

* solve load optimizer if some key not in optimizer

* variable name tmp_key to key

* add comment

* add Mask R-CNN model

* fix mask rcnn eval

* fix mask rcnn infer

* fix mask rcnn config

* fix infer config

* fix PadBatch

* fix PadBatchOp

Co-authored-by: Nroot <root@bjyz-sys-gpu-kongming0.bjyz.baidu.com>

* add export_model and deploy

* fix travis-ci

* update CMakeList & linux doc

* update by comments

* adapt new im_shape im Mask R-CNN-FPN

* fix training

* split yolov3 loss using paddle op

* add sync_bn and modify list to LayerList to use sync_bn, add missing op, support cutmix op in dataset, modify reader to use new ops

* modify code according to review

* modify code to run eval.py successfully

* modify code to run eval and train successfully

* modify code to use mixup

* rebase code on lastest dygraph

* modify code to run in sync_bn mode

* modify code according to review

* modify target size of ResizeOp

* update mask_rcnn_fpn model

* update smooth_l1_loss

* update smooth_l1 and sigmoid_cross_entropy_with_logits

* fix relu name

* 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

* update YOLOv3 config

* add matrix nms api

* add test error in matrix nms ut

* modify code according to review

* modify matrix nms api

* add yolo_box and add unittest of yolo_box.

* update comment

* update sample code, call op in ppdet

* migrate roi_align and roi_pool to ops

* modify code according to review