Modernize codebase

[mrwunderbar666]

Code is still written for Python 2 and uses a lot of unconventional coding practices.

[mrwunderbar666]

@AymericFerreira please check whether my changes still work as expected. I would test it myself, but I currently don't have my rasperry + MCP4922 readily available

[AymericFerreira]

Hello, just wanted to give you a quick update. I have a problem to get it working and I don't really understand why. I don't think it is code related, because I don't have any error, I suppose it is how I set-up spidev, but because it worked good with the previous of the code I don't understand what I did wrong.
I will not have access to the module for the next 2 weeks. I will try to redo complete installation after this