Add enum to status field

[m-mohr]

Closes #16

The field descrption explicity says "One of the value listed here", so it seems it's meant to be an enum.

[emmanuelmathot]

I would tend to agree, but it is all about the semantics of the word chosen, so if we think all cases are covered, I am okay.

[m-mohr]

I can't think of anything else and we also didn't see any issues coming up in the last years, so I assume it's fine. And adding values to an enum is not that big of a deal either, I think.