Summary:
CrypTen is now a proper [PyPI package](https://pypi.org/project/crypten/0.1/), making installation one step: `pip install crypten`.
* update readme with new installation instructions
* add logo raw link so it renders on PyPI
* update license and project url in `setup.py`
* specific version of `torch` and `torchvision` now specified in `requirements.txt` and automatically installed via pip
We can now also track installation statistics via PyPI.
Reviewed By: vreis
Differential Revision: D19746436
fbshipit-source-id: 7c64fc473265ef80751e01c95f003fffe0427f16