v15: Add linked_spaces, country_code, hint and areas

[rnestler]

See #117

Checklist

• Tests added if applicable
• [na] README updated if applicable
• [na] CHANGELOG updated if applicable
• [na] If a commit includes a breaking change, include the string [breaking-change] somewhere in the commit message

[dbrgn]

@rnestler you requested a review, but there are many open questions, primarily regarding the version support. We currently have logic in the builder related to the desired target version. This hasn't yet been updated to v15 (i.e. we have new fields, but the API claims that it generates v14)... Also, we need to decide how to handle mixed support.

A good option would probably be to drop support for all but the latest and second-to-latest version. That would mean that we'd support v14 and v15 (but not v0.13). Supporting all three would work as well, but would mean that we'd need to add a lot more validation logic. In that case, we'd avoid complicated questions related to mixed mode etc.

Before we continue, we should probably merge #122, then rebase and merge #121, because that will allow us to implement the optional location more easily.

[rnestler]

Yeah I just wanted to make you aware of the PR. The open questions are in the ticket #117 as well.

[rnestler]

Can we go ahead and merge the PR's that just add new v15 fields and then start working on the new multi-version handling?