Add mAP metrics and cleanup data pipeline

This release introduces mAP metrics for COCO datasets and refactor of the data pipeline to make it more clear for users.

Add COCOEvaluator and cleanup data pipeline

• Cleanup and refactor data pipeline (#103, #88)
• Fix unittest for coco evaluator (#91)
• Add mAP Metrics and validation methods in tasks (#93, #89)

Backwards Incompatible Changes

• Rename YoloHead to YOLOHead (#82)
• Rename GeneralizedYOLOTransform to YOLOTransform (#103)

New Features

• Keep consistency of transform (#102)
• Add Transformer (TAN) based model structure (#75, #81)
• Support training with vanilla module (#87)
• Add Docs with Sphinx (#85)
• Decoupling path dependence in notebooks (#84)
• Allow loading of user-trained ultralytics models (#79) , thanks @dkloving
• Add PyTorch 1.8 to CI (#76)

Bug Fixes

• Bug fixes in read_image_to_tensor (#97) , thanks @stereomatchingkiss

Documents

• Add comments about requirements (#96)
• Replaced print statements with logging library (#95) , thanks @itsabhianant
• Update badges (#83)
• Add instructions of minimial PyTorch version (#74)
• Rename parameters to keep consistency (#82)