* clean code of s2anet

* fix for paddle==2.1.0

* remove debug info

* update comment

* reorganize the code, and fix bug

* fix typo

* remve comment

* reorganize code

* Revert "reorganize code"

This reverts commit 4f928c3a46b264ba8815978b914bf81a46b66b62.

* set weight

* set default config

* fix code style

* 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

* 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 S2ANet model for Oriented Object Detection.