Made changes to support Python 3 and PyTorch >= 0.4.

[Florian1990]

Hi,

I changed two things to get matrix-sqrt running with Python 3 and PyTorch >= 0.4. It should still run with Python 2 but not with PyTorch <= 0.3.

Thanks for providing these useful functions!

[Florian1990]

Added more changes to execute the script only when it is run directly but not when imported.

[msubhransu]

Thanks Florian!