Sahi

- faster Coco merging and category updating (59)

- increase coco split and yolo export speeds (58)
- reduce json export size (57)
- make multiprocess call optional (55)

- 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.