Initial stab at supporting systems that do not use 'python' as the Python 3 command

[jesseops]

yes we are backwards :(

Ubuntu currently still uses python for Python 2, while other distributions (e.g., Arch) use python for Python 3 and python2 for Python 2.

This is a quick fix that uses the platform module to derive information about the system, specifically if it's an Ubuntu system in which case we know how to handle specifying version.

[mirekys]

Hi, I can confirm that even on Arch there is a python3 symlink. I believe that
python3 is nowadays available on most distributions, so there is no need
for the command map as we can just replace python with python3.

[jesseops]

@mirekys great, I like that way better than the admittedly hacked/ugly bit of code I tossed in to handle the translation. I'll update the pull request.

[mirekys]

Thank you, looks good to me now, merging this. Happy new year :)