Add cams.get_mcclear function

[AdamRJensen]

• Closes #xxxx
• I am familiar with the contributing guidelines
• Tests added
• Updates entries to docs/sphinx/source/api.rst 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.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.

Add a function to retrieve CAMS McClear clear-sky radiation as previously unsuccessfully attempted in #271, #274, #279.

[AdamRJensen]

@wholmgren I'm back! This time using GitHub Desktop, so hopefully, the code should have Unix end of line characters.

I'm unsure of why the previous commits show up in the this pull request... do you generally delete a forked repository after a successful pull request and refork it for additional pull requests?

I've asked the developing team of the CAMS radiation and McClear services, and have been informed that there is and will not be any demo API email/access. So if tests have to be implemented, we need to register a PVLIB email. Only a registered email address is necessary and no password will ever be public.

The function includes some very convenient features, including the label, integrated, and map_variable arguments, making it very intuitive for Python users. I'd very much like a critical look at the function and feedback on how it can be improved.

[mikofski]

Hi @AdamRJensen, thanks for this contribution!

I'm unsure of why the previous commits show up in the this pull request... do you generally delete a forked repository after a successful pull request and refork it for additional pull requests?

Sometimes previous commits show up if your branch is not sync'd with master. Also it looks like this PR is from your "master" branch of your fork rather than a "feature branch" which in my opinion makes it more difficult to manage your pull requests.

1. create a new feature branch on your laptop from the HEAD of your current working branch, (looks to me like you're working out of the master branch of your fork: AdamRJensen:master)

   path/to/pvlib (master)$ git checkout -b cams_macclear  # or some other descriptive name
   path/to/pvlib (cams_macclear)$
   

2. now force your master branch to resync with pvlib-python:master so they are mirrors.

   path/to/pvlib (cams_macclear)$ git checkout master
   path/to/pvlib (master)$ git pull -f git@github.com:pvlib/pvlib-python.git master  # overwrites your existing master branch
   path/to/pvlib (master)$ git push origin master  # update your online GitHub pvlib fork with latest master
   

3. now go back to your feature branch and merge master to make sure you have the latest changes. This should remove those extra commits you're seeing.

   path/to/pvlib (master)$ git checkout cams_macclear
   path/to/pvlib (cams_macclear)$ git merge master  # you may need to resolve a conflict, sometimes in whatsnew
   path/to/pvlib (cams_macclear)$ git push -u origin cams_macclear  # start tracking this branch on GitHub
   

4. now go online to GitHub and create a new Pull Request from your feature branch "cams_macclear" to pvlib-python:master reference this PR Add cams.get_mcclear function #1172, and then delete this PR. Sorry I don't think there's a way to redirect the source of PR, only the destination. But these steps will clean up this PR so you don't have a bunch of extra commits.

[mikofski]

@AdamRJensen also I'm wondering if this PR replaces the existing pvlib.iotools.ecmwf_macc package or if they can be combined someway or refactored? Perhaps worth commenting on if you can? thanks!