* add inference benchmark

* add lite demo

* move ssld model, test=document_fix

* fix typo, test=document_fix

* update README

* update doc, test=document_fix

* add citation

* update citation and ppyolo doc

* add docs for custom dataset, reader and model technical

* modify docs according to review, test=document_fix

* modify READER.md, test=document_fix

* Update QUICK_STARTED_cn.md (#1757)

fix typo

* cherry-pick #1757 and #1473, test=document_fix

* update solov2 some detail

* fix check paddle version

* Update CN README
* Change demo and update doc

Repalce fruit dataset with roadsign dataset, and update QUICK_STARTED, use PP-YOLO as demo, test=document_fix. (#1407)

* update INSTALL

* fix typo

* add demo image

* add use_gpu annotation

* fix link

* update style

* update style

* add install paddle

* use python3

* update INSTALL_cn.md

* update INSTALL_cn.md

* update INSTALL_cn.md

* fix typo

* add PPYOLO
Co-authored-by: Nlongxiang <longxiang@baidu.com>

* fix voc dataset and docs

* add custom datsset demo

Add image for visualdl board.

* Add libra-rcnn, GCNet and iou loss intro doc.

* add detailed doc
* add zh_CN doc of pssdet
* fix link

* add map_fps fig

* update YOLOv3_ENHANCEMENT.md
* update IoUloss and DropBlock configs for YOLOv3 related configs

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* Add inference benchmark
* Adjustment order
* Update some descriptions