Allow packages to use ISO 8601 dates in their PackageInfo.g

[fingolfin]

It would be nice if packages could also specify the release date in ISO 8601 format, i.e., as YYYY-MM-DD. This is less ambiguous than the current DD/MM/YYYY (which e.g. Americans may confuse with MM/DD/YYY).

Besides needing to modify lib/package.gi and the documentation, it may also be necessary to modify the package distribution.

This might be a good "first issue"?

[olexandr-konovalov]

Cf. also gap-system/gap-distribution#20.

I think we can implement this in a way that both formats will be permitted concurrently, and that ValidatePackageInfo will display an advice to switch to ISO 8601 (maybe at some info level, otherwise this will show up too often if #2726 is merged).

Indeed, not a problem to detect whether the date is in YYYY-MM-DD or DD/MM/YYYY format.

[cdwensley]

Date := "28/08/2018" is converted by GAPDoc to "28 August 2018" in a manual front page, whereas
Date := "2018-08-28" remains unchanged, which is not as nice. Perhaps @frankluebeck can comment?

[olexandr-konovalov]

I think that's a question to AutoDoc rather then to GAPDoc authors. AutoDoc extracts the date from PackageInfo.g, while GAPDoc - not.

[fingolfin]

Indeed, AFAIK does nothing with title pages. But we can certainly add support to ISO dates in GAPDoc, too. Alternatively, we could simply convert the date from ISO 8601 to the "old" date format on the fly while loading, thus preserving full compatibility with any code that might for whatever reason try to parse these dates.

[wucas]

I'm working on a PR to change ValidatePackageInfo so it accepts both formats.