DOC: stats.{circmean, circvar, circstd}: improve accuracy/clarity

[fancidev]

Reference issue

Toward gh-20240.

What does this implement/fix?

Improves the accuracy and/or clarity of the doc of the circmean, circvar, and circstd functions.

[j-bowhay]

Friendly reminder that for documentation-only PRs we can save some compute by adding [docs only] to the commit message
https://docs.scipy.org/doc/scipy/dev/contributor/continuous_integration.html#skipping

[fancidev]

@dschmitz89 If you could take a look when you have time it would be great!

[dschmitz89]

Thanks for the PR @fancidev . This looks good to me. Could you add a reference, for example Wikipedia? Then I would merge.

[fancidev]

Thanks for the PR @fancidev . This looks good to me. Could you add a reference, for example Wikipedia? Then I would merge.

Thanks for taking a look @dschmitz89 ! Let me locate the definition of those functions in Mardia and Jupp (1999) and add references accordingly.

[fancidev]

Reference added! @dschmitz89

[dschmitz89]

Thanks @fancidev .

[fancidev]

Thank you @dschmitz89 !