Issue #41 python version explicit

[Didou09]

Hi !

Thanks for developing this tool and making it available to all,

I will probably use it in the coming months, and figured I would starts by helping you close some issues.

Since I only discovered MRIO today I don't know yet how it works really and I can't yet contribute to in-depth code parts. So I looked for what looked like an easy issue to solve,

Main changes:

• Python minimum version is now explicit in the setup.py (for install time)
• Python current version is cheecked in the init.py (for run time)

Issues:

This PR aims at solving (at least partially) issue #41

I tried to keep it clean and simple, don't hesitate to let me know if this small contribution suits you

Regards Didier

[konstantinstadler]

Thanks for the suggestion. I went for a different solution then the init with making the python version explicit in setup.py (following https://stackoverflow.com/questions/49180733/what-is-the-appropriate-way-of-raising-an-error-for-having-the-wrong-python-vers ). Due to some code reformating, I cherry picked the other stuff from your setup.py manually. So this stuff is in in the next version. Many thanks!