Minor refactoring

[benman1]

Hi
Thanks a lot for this. I was looking around, and a lot of the other tools I found were a pain to set up, and this was easy in comparison.

The yolo3-one-file-to-detect-them-all looks good, but I propose a few changes to make this more useful as a library. For example, you could split the model loading and the detection methods. I've put my changes as a gist here.