adding a flag for relative directories in image

[daanelson]

adds the ability to preserve directory structure when pushing files to a cog image instead of just sticking everything under /src.

Main use case here is for pushing changes to an existing cog model from the root directory, so if you have a project structure where you have /module/important_model.py, running yolo ... -p module/important_model.py will push the model to /src/module/important_model.py instead of /src/important_model.py.

imo this is probably the main use case for yolo when not just placing everything under /src/

[anotherjesse]

Thanks @daanelson - I'll double-check the actual code tomorrow but I like the design - and think perhaps it should be the default