* [WIP] Keypoints inference on C2 models work

* Training seems to work

Still gives slightly worse results

* e2e training works but gives 3 and 5 mAP less

* Add modification proposed by @ChangErgou

Improves mAP by 1.5 points, to 0.514 and 0.609

* Keypoints reproduce expected results

* Clean coco.py

* Linter + remove unnecessary code

* Merge criteria for empty bboxes in has_valid_annotation

* Remove trailing print

* Add demo support for keypoints

Still need further cleanups and improvements, like adding fields support for the other ops in Keypoints

* More cleanups and misc improvements

* Fixes after rebase

* Add information to the readme

* Fix md formatting