Sphinx docs

[chsasank]

Fix #284

Idea is to fix the documentation build process of torchvision using sphinx.

Here's how docs will looks like: https://chsasank.github.io/vision/

TODO:

• Complete sphinx docs here
• Add build script to https://github.com/pytorchbot
• Remove vision docs from pytorch.org/docs

[fmassa]

I think this looks good, but I have no experience with sphinx so I can't comment on that. I suppose we also need to change something in https://github.com/pytorch/pytorch.github.io ?

[chsasank]

We'll fix pytorch.org/docs later by removing docs/torchvision in pytorch/pytorch.