* Add BottomUp HigherHRNet for pose.
* reverse xtcocotools to pycocotools

* fix voc eval

* remove debug code

* add comments

* update comment for collate_batch

* pose bottomup higherhrnet: data
* mv common function to ppdet modeling;
* fix code style

* add ttfnet enhance

* add doc

* fix pafnet training

* add pssdet model

* Add S2ANet model for Oriented Object Detection.

* add docs for custom dataset, reader and model technical

* modify docs according to review, test=document_fix

* modify READER.md, test=document_fix

fis the issue in function _get_shared_memory_size_in_M in the case of that there are multiple 'shm' space (#2434)

* update DataLoader & speed up Mask RCNN

* refine trainer

* support not pad gt in rcnn model

* add comment in reader

* update ppyolo_mobilenet_v3 large & small

* support visualdl in preprocess data

* support most preprocess op

* update solov2 some detail

* fix check paddle version