Polygon: closed and right hand rule?

[visr]

The Polygon type currently holds an exterior ring and one or more interior rings, but otherwise doesn't enforce much.

Currently it is not enforced that the first and last positions should be equal, or the right hand rule as in https://tools.ietf.org/html/rfc7946#section-3.1.6

Should we enforce these in this package? Or is it better to deal with those in packages such as GeoJSON.jl do you think?

[SimonDanisch]

That seems like a cheap enough check to just always do it, if it's required ;)

[aplavin]

Would be nice to check any nontrivial requirements like being closed. Any downsides to adding such a check?
I recently had an issue with wrong results from polygon manipulations, and only learned they need to be closed for operations to be correct after asking on slack (thanks @asinghvi17!).