Run tests against all supported Python versions.

[yezyilomo]

This is just a suggestion, I used to run tests against the python version I was using on my machine before pushing to GitHuB, using this approach sometimes I found my self breaking my packages on other python versions unknowingly by using some features which are not compatible with some versions of python usually older versions because on my machine I was usually using the latest version. So to avoid this I started using tox and CI to tests my packages against all versions of python which I support before merging changes to master branch this way I would know whether I’ve broken something or not.

So my suggestion here is to add a way to run tests against all versions of python which you want to support so that u don’t break things on other versions unknowingly, don’t just assume whatever runs on python version on your machine will run on other versions too.