* add centertrack base codes

* fix deploy and docs

* fix tracker

* fix

* fix pre_img

* fix deploy

* fix

* remove duplicate backbone variant, test=document_fix

* fix slice_image deploy infer index

* add slice infer for smalldet

* add slice infer for smalldet

* fix slice infer

* fix doc, test=document_fix

* fix eval and configs

* add slice dataset loader

* fix deploy

* fix docs, test=document_fix

* update docs, test=document_fix

* fix infer dataset download and label

* add doc, test=document_fix

Besides removing unnecessary imports, this also fixes the missing logger module in test_architectures.py within the static directory.

* add config for jde and deepsort, add engine metric tools

* add mot_metrics

* fix configs engine and others

* fix configs others

* move configs

* fix ap_per_class, fix doc

* fix test_mode, seqs

* fix test_mode to metric

* fix JDE arch metric

* clean requirement

* add to requirement

* add mot data

* fix operators, source

* fix data source transform

* fix parse_dataset register_op

* fix scale_factor, RandomAffine

* add assert for check

* fix ci

* add ttfnet enhance

* add doc

* fix pafnet training

* refine trainer

* refactor rcnn, test=dygraph

* add mask_rcnn, test=dygraph

* add Faster RCNN & Faster FPN, test=dygraph

* update according to the review, test=dygraph

* add solov2 dygraph model, test=dygraph

* ppdet installable

Merge dygraph branch into master branch.
Co-authored-by: NFDInSky <48318485+FDInSky@users.noreply.github.com>
Co-authored-by: Nsunxl1988 <47514455+sunxl1988@users.noreply.github.com>
Co-authored-by: Nwangguanzhong <jerrywgz@126.com>
Co-authored-by: Nwangxinxin08 <69842442+wangxinxin08@users.noreply.github.com>
Co-authored-by: Nwanghuancoder <wanghuancoder@163.com>
Co-authored-by: Ncnn <liuhui29@baidu.com>
Co-authored-by: NGuanghua Yu <742925032@qq.com>
Co-authored-by: NKaipeng Deng <dengkaipeng@baidu.com>
Co-authored-by: Nroot <root@bjyz-sys-gpu-kongming0.bjyz.baidu.com>

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* refine cocoapi import

* fix infer when anno_path is None

* 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.