Move surface orientation calculation from tracking.singleaxis to new function; switch to Marion & Dobos 2013 equations

[kandersolar]

• Closes Consider extracting the surface orientation calculation in pvlib.tracking.singleaxis() to its own function #1471
• 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.
• 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.

[wholmgren]

As a follow up, should we remove https://github.com/pvlib/pvlib-python/blob/master/docs/tutorials/tracking.ipynb? Looks like a lot of work to bring that notebook up to date with the current implementation and the newer features.

I'd also recommend updating the PR title to reflect the use of new equations.

[kandersolar]

should we remove https://github.com/pvlib/pvlib-python/blob/master/docs/tutorials/tracking.ipynb?

Ugh, maybe. I hate to delete useful info, even if the specific implementation doesn't match the current pvlib. If there is effort to spend, I think I'd rather put it into a new User Guide page to replace that notebook instead of updating the notebook itself. Or maybe improved gallery examples as suggested in #1077 (review).

I'd also recommend updating the PR title to reflect the use of new equations.

Good point. Wish I had done that before the title got used for the squashed commit message. Oh well!

[wholmgren]

I agree that a user guide page and/or gallery examples are better than updating the notebook.

I didn't pay much attention to this PR since the title suggested that it was just a matter of moving code from one function to another :)

[kandersolar]

I didn't pay much attention to this PR since the title suggested that it was just a matter of moving code from one function to another :)

Yep, that's my bad. Please feel free to point out anything you wish had been done prior to merging and I will happily rectify it!