Demo notebook fails due to recent changes

[Eisenh]

I think the recent changes to the feos structure broke this demo. It fails at the imports

from feos.si import *     # SI units and constants
from feos.eos import *    # equation of state objects
from feos.pcsaft import * # parameter objects

And when replaced by
from feos import *
The next cell throws an error:
NameError: name 'SIArray1' is not defined

[g-bauer]

Thank you very much for the issue. I'll add an updated version of the notebook when I find the time. Until then you find (hopefully) up-to-date notebooks for FeOs in the examples folder of the main repository.