* update 2.1 readme

* update en doc, test=document_fix

* update doc, test=document_fix
Co-authored-by: NGuanghua Yu <742925032@qq.com>

* update slim models and benchmark

* Add document about how to export ONNX model

* update det infer benchmark log

* Update README.md

* s2anet fix export and deploy

* remove redundant code

* fix cpp for s2anet deploy

* fix bug of get_categories

* rename poly_to_rbox to poly2rbox

* add some comment for function

* add inference benchmark

* add lite demo

* add ext_op build doc, test=fix_document

* add note for JetPack version with machine

* fix path of script, test=document_fix

* update for ci-travis, test=document_fix

* add benchmark, test=document_fix

* update style of number, test=document_fix

* add difference of dynamic shape and fix shape

* fix paddle inference name problem, and update doc

* set default value

* fix inference lib name in static

* update deploy doc, fix build error of windows

* add annotation of PADDLE_LIB_NAME

* set min_subgraph_size=33 as default, fix bug of fcos_dcn_r50_fpn_1x

* support not pad gt in rcnn model

* add comment in reader

* Update install doc and deploy doc.

* fix doc link, test=dygraph, test=document

* update solov2 some detail

* fix check paddle version

* update cpp build script

* rename document and update script

* set WITH_MKL=ON for pass CI

* set WITH_GPU=OFF and WITH_TENSORRT=OFF for pass CI