add ASTM E1036 parameter extraction

[mdeceglie]

• I am familiar with the contributing guidelines
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
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This PR adds the ASTM E1036 methods for extracting performance parameters from IV curves. The code has been adapted from https://github.com/NREL/iv_params

[mdeceglie]

Here is a start at adding ASTM E1036 IV curve parameter extraction. Open to any and all feedback including naming of function/module/parameters. The original code was object-oriented and included plotting functionality. I have simplified it to a stand alone function to avoid opening a whole can of worms about plotting and to align with the overall low-level functional building block approach of pvlib, but we can re-evaluate these choices if there is interest.

[kandersolar]

I agree plotting should not be in pvlib itself, at least at this time. Could be a good fit for the example gallery. I'm neutral on the pvlib.ivtools.params name, don't love it but can't think of anything better.

[adriesse]

I think everything could all be calculated with numpy only without many changes, if that is of interest.

[mdeceglie]

Interesting suggestion. I don't think I will have time to tackle it, but if you feel it makes a sufficient improvement please go for it. Tests are in place now so it should be easy to verify that it has worked.

[cwhanse]

@mdeceglie fyi we are still working out language for the copyright renewal. Thanks for your patience.

[kandersolar]

A few sphinx nitpicks but otherwise LGTM pending the copyright question.

I'm okay with the new pvlib.ivtools.params module name but I'm not really familiar with this area. Can we imagine any other related functionality we may want to add in the future that might make us wish we had chosen a different module name?

[mdeceglie]

It might make sense to move this into the utils module which is described as containing "utility functions related to
working with IV curves, or fitting equations to IV curve data." I think this qualifies as "working with IV curves".

[adriesse]

Just a few comments, not a complete review.

[kandersolar]

@cwhanse OK to merge?

[cwhanse]

@cwhanse OK to merge?

Yes after the whatsnew conflict is resolved of course.