* modify links about master, test=document_fix

* modify develop to release/2.1

* correct links, test=document_fix

* fix eval snapshot_epoch

* 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

* 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 static notice

* fix path of script, test=document_fix

* update for ci-travis, test=document_fix

* 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

* replace clock by chrono for accurate elapsed time

* replace clock by chrono for accurate elapsed time in dygraph