Warn about undocumented non-private APIs.

[reitermarkus]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

All non-private APIs should actually be documented, not just marked.

Also, automatically hide #hash, #inspect and #to_s, as well as automatically add @deprecated based on odeprecated/disabled.

[MikeMcQuaid]

Great work again @reitermarkus, appreciate you getting these docs looking nicer/better.

[MikeMcQuaid]

👍🏻 to 🚢 once CI is 🟢