* add gn head fpn, test=dygraph

* add gn for cascade

* update gn readme, test=dygraph

* from_config hrnet, test=dygraph

* update hrnet modelzoo, test=dygraph

* fix crash bug when using cpp infer, test=dygraph

* update PaddleServing deploy, test=dygraph

* Update export_model.py

* Update export_model.py
Co-authored-by: Nqingqing01 <dangqingqing@baidu.com>

* update cascade, test=dygraph

* clean code, test=dygraph

* add cascade_rcnn, test=dygraph

* update according to reviews, test=dygraph

* support dy2static, test=dygraph

* fix bbox_num 0 after nms, test=dygraph

* add copyright, test=dygraph

* add fp16 and fleet api

* add instructions for fleet api and fp16

* modify example of fleet api

* modify docs of fleet api

* fix_quickstart_doc

* fix RCNN dygraph to static

* fix problem due to empty bbox_pred and modify ppyolo docs, test=dygraph

* modify post process to avoid dy2st problem

* fix fcos ttfnet yolov3 config

* fix doc image, test=document_fix

* add quickstart doc, roadsign dataset

* add dygraph quant

* add ppyolo r18vd mbv3, yolov3 r50vd

* modify TestReader of ppyolo mbv3 r18vd

* add clip to avoid nan, modify ema to apply ema on bn mean and bn var

* fix code resulting in nan

* add yolov3 r50vd dcn configs

* finish yolo_series and fix some problems

* hide --bias flag and modify docs

* modify --bias and fix deploy/python/infer

* fix model_zoo package for configs directory structure change

* update README

* update prepare dataset and deploy document, test=dygraph

* simplify CMakeList, test=dygraph

* add cpp doc link, test=dygraph

* remove WITH_STATIC_LIB, test=dygraph

* update doc, test=dygraph

* fix cmakelist, test=dygraph

* split EXPORT_MODEL.md, update READEME.md, add QA on deploy README.md, test=dygraph

* Using same env as paddle_inference_lib when deploy, test=dygraph

* fix typo, test=dygraph

* fix load_weight and no bbox output

* fit ttfnet

* fit for YOLOvd/PPYOLO/SSD

* eval in train