Even though this is nice in isolation, I think it would be slightly more consistent to add an `Unsubscribe` resource and then just have `Delighted::Unsubscribe.create(person_email: '...')`.

We'll have an `Delighted::Unsubscribe.all` operation too at some point, so I this way would accomodate that better in the future. 

(We definitely want to revisit the API design before the next major (breaking) version of the API. Lots of ideas for making it more elegant and simple overall.)