Drop Python 2

[carlthome]

IIRC future and six were for the Python 2 -> 3 migration. As Python 2 has passed EOL it's probably not necessary to mention it anymore.

[craffel]

If we are going to do this, we need to remove imports/uses of six and future from the library and should probably add python_requires to the setup.py

[carlthome]

If we are going to do this, we need to remove imports/uses of six and future from the library and should probably add python_requires to the setup.py

Ah, good catch! I got fooled by six and future being transitive dependencies and thus the tests passed.

[craffel]

Thanks!