Drop support for EOL Python 2.6

[hugovk]

Pytest and Py have both dropped Python 2.6 as it's been EOL for 4 years.

Also remove some redundant Python 3.2 code (also EOL and looks like it's already dropped), some minor code cleanup, and add a Python version badge.

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[RonnyPfannschmidt]

well done, thanks 👍

[jurko-gospodnetic]

something broken in our bleeding edge code? related tests seem to be failing...

[hugovk]

Yep the pytestmaster and pytestfeatures build jobs are also failing on latest master:

https://travis-ci.org/hugovk/pytest-xdist/builds/319594409

[nicoddemus]

I suspect this is breaking because the output has changed and now includes the progress indicator in pytest-3.3, so the code which parses the output is not detecting what it intends to.

[hugovk]

Thanks, I've created #260 for that, as it's unrelated to this PR.

[nicoddemus]

Thanks @hugovk. I'm merging this then, and open a PR shortly for #260.

[nicoddemus]

@hugovk 1.21.0 has been released, thanks again for the PR!