Drop support for Python 2.7 (and 3.5)

[jugmac00]

The build currently breaks on Python 2.7, as a transitive dep is no longer Python 2.7 compatible.

While we could pin the dependency, maybe it is about time to move forward?

[petri]

Yes, why not. Anyone needing Python2 support will be able to just use 1.3.1.

[petri]

Builds pass again. Metadata, build configs and docs changed to indicate Python3 only status from now on. There's things we still could & should do I am sure so not closing this yet.

But since some badges use pypi as a source of truth, should preferably push a release sooner rather than later.

[jugmac00]

I have a bit of spare time tomorrow. I will look into this. Also, I'd like to run https://github.com/asottile/pyupgrade on the source code.

What is your take on support for Python 3.5? It is EOL since September. Python 3.6 brought f-strings, and also typing (#50) is more convenient with Python 3.6+ as then type annotations for variables were introduced.

[petri]

What is your take on support for Python 3.5? It is EOL since September. Python 3.6 brought f-strings, and also typing (#50) is more convenient with Python 3.6+ as then type annotations for variables were introduced.

I would say let's require 3.6+ while we're at it.