Sahi

- faster coco dataset indexing (53)
- category remapping feature for coco datasets (53)
- fix export_as_yolov5 paths (52)

- make some dependencies optional
- fix some coco utils

- add new coco utils. check [COCO.md](https://github.com/obss/sahi/blob/main/docs/COCO.md) for example usages.
- add [slicing notebook](https://github.com/obss/sahi/blob/main/demo/slicing.ipynb).
- fix some mmdet/numpy warnings.

- add new coco utils (https://github.com/obss/sahi/pull/42). check [here](https://github.com/obss/sahi/blob/main/tests/test_cocoutils.py) for example usages.

- refactorized [Coco class](https://github.com/obss/sahi/blob/3ad54d682a8ab2c98abfd88f30c80a85c19d1eb1/sahi/utils/coco.py#L726), added [CocoVid class](https://github.com/obss/sahi/blob/3ad54d682a8ab2c98abfd88f30c80a85c19d1eb1/sahi/utils/coco.py#L1508)

- added [coco_error_analysis.py](https://github.com/obss/sahi/blob/main/scripts/coco_error_analysis.py) script:

bash
python scripts/coco_error_analysis.py results.json output/folder/directory --ann coco/annotation/path


will calculate coco error plots and export them to given output folder directory.

If you want to specify mAP result type, set it as `--types bbox mask`.

If you want to export extra mAP bar plots and annotation area stats add `--extraplots` argument.

If you want to specify area regions, set it as `--areas 1024 9216 10000000000`.

* fix a sliced prediction bug happening on small images