* 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 eval snapshot_epoch

remove doubled words

* fix voc eval

* remove debug code

* add comments

* update comment for collate_batch

* add ppyolov2

* fix bugs and modify docs

* modify code and doc according to review

* fix bugs while resolving conflicts

* update README

* update doc, test=document_fix

* add citation

* update citation and ppyolo doc

* add PP-YOLO tiny

* support ppyolo for kunlun

* update ppyolo_mobilenet_v3 large & small

* add ppyolo_voc

* add ppyolo mobilenetv3

* unify log_smooth_windows and log_iter

test=develop

* remove duplicate log_iter

* remain mobile yml, since they are soft-link

test=develop

* expand ratio=2.0 & add ppyolo_2x_bs12.yml

* sync TrainReader.batch to global train_batch_size

* update version require for ppyolo

* ppyolo_tiny to ppyolo_r18vd

* polish AP description

* add PP-YOLO README en

* add ppyolo_tiny

* add COCO test-dev eval config and doc