Include standard Duration pattern that matches the one used for JSON

[maciejjarzynski]

The standard Duration pattern described in the docs:
https://nodatime.org/2.3.x/userguide/duration-patterns
is -D:hh:mm:ss.FFFFFFFFF
whereas the JsonConverter in
https://github.com/nodatime/nodatime.serialization/blob/edf88349e54ab63f06266a9c864edfa1ba6503cb/src/NodaTime.Serialization.JsonNet/NodaConverters.cs#L102

has a pattern -H:mm:ss.FFFFFFFFF.
Does this serve any purpose, or it can simply be DurationPattern.Roundtrip there?

[jskeet]

I honestly don't remember the origin of using this instead of the standard pattern, but I'd argue that we shouldn't change it at this point; it would be a breaking change for stored information for little benefit.

Rather than change either, I think it would probably be more useful to add an extra standard pattern that corresponds with the JSON one. Does that sound like a reasonable compromise?

[maciejjarzynski]

Yes, for the sake of compatibility that would be an option, thanks ;)

[jskeet]

Righto - renamed the issue for what it's turned into just for my convenience :)