PySQM needs to be updated to Python3

[jscheidtmann]

Since Python2 has been sunsetted on Jan, 1st, 2020, i.e. no updates since then. PySQM needs to be updated to use Python3.

[dario-pilori]

On http://unihedron.com/projects/darksky/cd/RPi/, there's a version of PySQM ported to Python3.

I pushed this version on my PySQM fork, integrating the 2022 changes in PySQM code:
https://github.com/societa-astronomica-g-v-schiaparelli/PySQM/tree/pysqm3

This code needs to be tested, but, at least, it is a good starting point.

[seanmccully]

I did open a PR for this as well, I have it running on windows with Python 3.11

[seanmccully]

it might make sense to put the Python 2 on a different branch, also didn't see the other fork before I did mine.

[mireianievas]

Created 2.7 branch out of commit #78e1271ff14f5c253024bf8c0fa6f99c3a30b17c