Make it installable by pip

[hsiao yi]

As title, with this change, we can make this tool more useful.

[Abdul Karim]

I agree!!!!

[Esben Jannik Bjerrum]

Thanks for the interest in the code. I would encourage you to take a look at the molvecgen package.

https://github.com/EBjerrum/molvecgen

It has an installer, but is not on pip as such.

However, can be installed with pip with

python -m pip install git+https://github.com/EBjerrum/molvecgen