Show value of enums in documentation

[Geod24]

The value of enum is quite important and should be displayed in the doc.

As an example, consider: https://vibed.org/api/vibe.http.status/HTTPStatus I wanted to return a 400 but use HTTPStatus. However, the lack of value (and me not knowing the exact name in the specs) means that opening the code was the fastest / best thing to do.