Include inherited methods for instruments (mixin preparation)

[BenediktBurger]

          I'd include a task for updating driver documentation `.rst` files for all drivers to inherit `SCPImixin` so the SCPI properties are included on their instrument driver page. Let me know if you'd like to split up the tasks.

For instance, for class SomeSCPIinst(SCPImixin, Instrument), the following would inherit properties for documentation up to Instrument, so Instrument isn't included but SCPImixin functionality is:

#########################
Some SCPI inst
#########################

.. autoclass:: pymeasure.instruments.example.SomeSCPIinst
    :members:
    :show-inheritance:
    :inherited-members: Instrument

Originally posted by @mcdo0486 in #905 (comment)

I propose to add this line to all classes, such that they will show methods inherited by their mixins, whichever might come.

One point, though: "show-inheritance" will show all these parent classes, such that you could check them in order to get the methods.