Clear up torchvision version

[vmarois]

had to use torchvision 0.2.0 to get the doc build successful for the first time but seems to be causing an error with Resize (wasn't showing up with 0.2.1)

[vmarois]

I should have clear up what it happening:

• The installation of the framework (through python setup.py install) should require the latest version of torchvision (currently 0.2.1) as we get an error: AttributeError: module 'torchvision.transforms' has no attribute 'Resize' with torchvision<=0.2.0. It's also best if we do not have that version constraint at all.
• The documentation build requires torchvision<=0.2.0 as 0.2.1 seems to cause the error: AttributeError: module 'PIL.Image' has no attribute 'LANCZOS'. I am not sure where this is coming from. My guess is on the docker environment of readthedocs.

So the current solution is to not use python setup.py install for the doc build (which is slower anyway), but to instead point to a requirement file containing torchvision==0.2.0. This allows to separate these 2 build processes.

Closing this for now.