* update blazeface mAP, add pre-training model.

* modify links about master, test=document_fix

* modify develop to release/2.1

* correct links, test=document_fix

* add fpn for blazeface

* update mot doc config, test=document_fix

* update citations

* update title, test=document_fix

* update link develop -> release/2.1. test=document_fix

* fix mot doc, test=document_fix

* fix mot16 doc, test=document_fix

* fix image_shape in export_model

* fix infer bug of s2anet

* update slim models and benchmark

* support no label training

* fix load_crowd

* update to fit rbox

* add empty_ratio

* update configs

* support mask rcnn

* clean drop_empty for mot & keypoint

* refine is_crowd

* fix ffmpeg video infer, fix doc, test=document_fix

* fix ffmpeg installl, test=document_fix

* fix mot_source

* fix mot_source, test=document_fix

* fix jde negative coords

* update jde model zoo

* describe format for some txt, test=document_fix

* fix mot doc

* remove image_lists, fix all mot docs, add custom data

* fix doc, test=document_fix

* fix dov

* fix doc format, test=document_fix

* add video infer for TestMOTReader

* format, test=documment_fix

* update install docs

* fix slim doc,test=document_fix

* add fairmot

* rename pretrain_weights

* add comments; reuse focal loss and convnorm

* update comments

* fix hsv randomaffine

* fix nms return_index

* fix gt_ide by tid_start_index

* add deepsort configs comments

* fix doc, add readme_cn

* fix doc

* fix jde doc and metric test_mode

* add image_lists

* add readme_cn

* fix eval snapshot_epoch

* 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

* 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