Adopt NumPy doc-string style guide

[bjlittle]

See

• https://numpydoc.readthedocs.io/en/latest/format.html
• https://www.sphinx-doc.org/en/master/usage/extensions/napoleon.html

[github-actions]

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[HGWright]

NumPydoc added in #288 and #277 currently tracks the individual outstanding ignored checks.