Clean up demo notebooks

[NoraLoose]

I think it would be a good idea to clean up the notebooks in demo_notebooks a little bit, especially because we are planning to include them on the website. A few suggestions:

• Removing the commented out code. Let's keep these notebooks tidy!
• Moving some of the class and function definitions to modules to make the notebooks more compact.
• Including a short introduction at the beginning of each notebook to summarize what will be done.
• Possibly including Figure 1 and 2 from the Supplementary Information (which show the network architectures) of the ClimSim paper at the beginning of the two notebooks cnn_example.ipynb and mlp_example.ipynb.
• Including a few more figures on the way (if possible), and make the figures look a little bit nicer. A website / notebooks with nice figures will be read by more people - no joke!

I am happy to help with this, if other people agree with the suggestions above. @jerrylin96 @cisaacstern?

[cisaacstern]

Great suggestions, all of which make sense to me but also doesn't necessarily have to block #15 IMHO.

Moving some of the class and function definitions to modules to make the notebooks more compact.

This is definitely a good idea, and will also allow us to unit test all of these functions/classes with pytest.

To start this process, I would suggest adding a new module in the climsim_utils directory, and moving any functions / classes from the notebooks into that module. Then when the package is pip-installed, those objects will be available for import with:

from climsim_utils.new_module_name import function_a, class_b, etc

As a subsequent step, we'll want to think about how to structure these modules into function groups (xref #17). But to start just having them out of the notebooks is a good place to start.