the script to transfer json to yolo

[peiliu0408]

as mentined in README file, the yolo family using a unique label formatting, it would be more convenient if a simple script to generate yolo style annotation are provided, which can transfer arbitary keypoints (like hand, not 17 keypoints) dataset.

[fengxiuyaun]

yes. you can also ues only one pose(others are 0)