Add PVSPEC spectral correction factor model

[RDaxini]

• Closes (partially addresses Add new spectral factor models #1950 and Google Summer of Code project summary: Implementing new spectral corrections in pvlib #2065)
• I am familiar with the contributing guidelines
• Tests added
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

This model is one of the spectral correction functions suggested in the cited issues (#1950 and #2065).
Docs: https://pvlib-python--2072.org.readthedocs.build/en/2072/reference/generated/pvlib.spectrum.spectral_factor_pvspec.html

[echedey-ls]

There are a few things that need to be done first:

1. Separate the implementation into an existing or new file. E.g.: pvlib/spectrum/mismatch.py
   (That's moving the current function you have to there, modifying the needed __init__.py files too; I think your current test_pelland.py file is not a test, it seems like an implementation of the model)
2. Create tests under pvlib/tests/test_spectrum.py. Prefix tests with test_ as @cwhanse noted, so they can be discovered automatically by pytest. I don't know exactly the pytest command to run exactly one test by name, but you could run that file by itself there. Or keep that file temporarily.

In general, you may want to see some PRs that add new functions as a reference. For example, #2041 is simple IMO. There are many more of course, it's just I'm too selfish to look for other ones (/sarcasm)

I've been inspired by #2067 to do a post blog regarding my setup. I know I wrote too much, but in case it helps you, check it out here.

[RDaxini]

@echedey-ls @cwhanse Thank you for the help. I think I have updated the files with the correct names now (and also put the functions in the right places)
The tests that I have added into test_spectrum.py so far have passed, but are there any additional tests I need?
Something else I am unsure about is documentation. I added in text for the docs into mismatch.py but when I try to view the build here it looks just like the pvlib homepage rather than the text I included in mismatch.py so I wanted to ask how/where do I write/set up the documentation correctly?

[echedey-ls]

Well done @RDaxini , it looks good!!

how/where do I write/set up the documentation correctly

Yeah, documented functions aren't discovered automatically, you need to specify in a rST file the function. In general, these files are under docs\sphinx\source\reference. Specifically, for this model you would add to docs\sphinx\source\reference\effects_on_pv_system_output\spectrum.rst.

I will review in short some of the common typos we all make in the docstrings.

[echedey-ls]

Some general feedback. I don't want to overwhelm you, but I've left a fair amount of comments.

[echedey-ls]

Don't worry @RDaxini , we've all been there.

Btw, can you double check the "sodapro" link is what you intended? http://www.sodapro.com/gl/web-services/atmosphere/linke-turbidity-factor-ozone-watervapor-and-angstroembeta

It doesn't work (404). Ah, and Sodapro looks like a sandblasting company?

[kandersolar]

I believe https://www.soda-pro.com/ is the correct website ;)

[cwhanse]

Editorial mostly, I think that matching output type to input type has slso been raised by others.

[echedey-ls]

@kandersolar @AdamRJensen or @cwhanse can you approve the workflows on this PR?

[kandersolar]

@RDaxini one last thing is needed: a "what's new" entry for v0.11.0. Can you make a new bullet point under Enhancements in v0.11.0.rst, and list yourself in the Contributors list at the bottom of the file?

[kandersolar]

LGTM with one minor syntax edit. Thanks @RDaxini!

[RDaxini]

Thanks for all the reviews @echedey-ls @cwhanse @IoannisSifnaios @kandersolar