Drop Python 2 support in PyScaffold v3.1

[FlorianWilhelm]

PyScaffold is a tool for creating new Python projects and Python 3 surely has been for quite a while the right version to start a new project. Also due the a bug in setuptools the current version 3.0 of PyScaffold has no Python 2 support right now and there were no complaints about this.
We could officially drop the Python 2 support in PyScaffold 3.1 and get rid of six, unnecessary __future__ imports in templates and the code of PyScaffold itself. This would clean things up.

[abravalheri]

To be sincere, since the test suite is intrinsically broken with 2.7, all the last changes might be incompatible anyway...

[FlorianWilhelm]

Okay, sounds like we have a decision then ;-)

[FlorianWilhelm]

Since we have never had Python 2 support in version 3.0 we can drop it in version 3.1 officially without violating semantic version. I wouldn't want to wait for version 4.0 for that.

[FlorianWilhelm]

Since the six and all __future__ imports where removed this ticket can be closed. As we go we should start using more Python 3 features and make things even more pythonic.

[abravalheri]

Unfortunately we have to wait 3.6 to be the base line to use f-strings 😝