rename all Hrnet to HRNet

* Add BottomUp HigherHRNet for pose.
* reverse xtcocotools to pycocotools

* fix voc eval

* remove debug code

* add comments

* update comment for collate_batch

* update ssd loss, make it faster test=develop

* update comments, test=develop

* ssd loss, fix bug when no object, text=develop

* pose bottomup higherhrnet: data
* mv common function to ppdet modeling;
* fix code style

* update 2.0.1

* add script of dota_2_coco

* add args for dota_to_coco

* add script to generate test result of dota

* add loss weight for s2anet

* fix dy2st for s2anet

* fix code style

* remove rbox-iou-ops dependence

* fix some docs error

* fix name of ConvNormLayer for fcos solov2

* fix name in other head convbn

* fix yolo name, fix ttf_head name, test=document_fix

* add ttfnet enhance

* add doc

* fix pafnet training

* add ppyolov2

* fix bugs and modify docs

* modify code and doc according to review

* fix bugs while resolving conflicts

* add PP-YOLO tiny

* add pssdet model

* fix name of pretrain weights

* format, test=document_fix