Update to newer API version

[kochsebastian]

Hey, you hinted in other issues that you are planning to release yolov3 soon. I personally just want to get yolov2 running and compare it to different models in the model zoo. Therefore, I am on a much never API version than you. Integrating your files into the new API version is quite a challenge for me because just adding your code will break the pipeline. I tried a little over an afternoon to merge the two versions but too much has changed since your implementations. I really don't want to revert back to your API version. Things like simultaneous training and evaluation for example are just great in the new API version. So when release yolov3 will you also update to a newer API version, if so would it be possible to release it early for yolov2 that would be wonderful