Set save_dir = log_dir in train.py

Add example of hyp yaml

onnx should be 1.6.0

for smoothly export model to onnx, onnx should be 1.6.0

In torch==1.5, the import of the API has changed. Although it does not interrupt the operation of the program, it seems to me to be an implicit error and may throw an exception in later versions.

added logic in train.py __main__ to handle resuming from a run

Uncomment plot_lr_scheduler in train() and pass log_dir as save location

Delete redundant thrid party library

I submitted it once in your yolov3 project, you seem to accept it? I'm not sure. I'll submit PR again.