YoloV8相对于YoloV5的改进点：
- Replace the C3 module with the C2f module.
- Replace the first 6x6 Conv with 3x3 Conv in the Backbone.
- Delete two Convs (No.10 and No.14 in the YOLOv5 config).
- Replace the first 1x1 Conv with 3x3 Conv in the Bottleneck.
- Use decoupled head and delete the objectness branch.
- anchor free.
