* add ssd_vgg16_120e_coco

* fix dygraph

* refine keep_ratio in ResizeOp

* update dygraph export model

* delete get_export

* adapt faster and cascade

* update reader in dygraph

* update dataloader some detail

* fix num_classes with background

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

* refactor dygraph & add mask rcnn fpn

* fix initialization & minor update

* refine architecture of mask_rcnn

add train&eval 
add reader padding 
add new config 

clear directories & files for dygraph branch 

* Update docs
* Update README.md

* optimize python path

* add yolov4

* update check config

* fix slim/xx

* add devices_num on reader

* refine capacity value

* refine bufsize

add libra rcnn, including
  * libra loss
  * libra fpn(bfp)
  * libra sampling

* 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.

* Add cascade_rcnn_cls_aware_r200_vd_fpn_dcnv2_nonlocal_softnms model on oidv5 and obj365.
* Add obj365 config annotation
* Update docs.

* update code & doc

* add multi-scale test

This reverts commit b591cc133ca04dc1ed50631c8d24031bb97db18b.

* unify reader to dataloader

* add check_version

* Support finetune by custom dataset

* add finetune args

* add load finetune

* reconstruct load

* add transfer learning doc

* add fruit demo

* add quick start

* add data preprocessing FAQ

* Add benchmark (fps) in MODEL_ZOO doc

* fix add map_type