Rearranging `Data.X.Relation`

[MatthewDaggitt]

We need somewhere to put propositions not just binary relations over compositional data such as List. The suggestion from #556 is to move the existing Data.X.Relation hierarchy to Data.X.Relation.Binary and so make room for Data.X.Relation.Unary (and even Data.X.Relation.Trinary in the case of #529).

The old modules would be deprecated but still exist and at some point we'll get around to creating a WARNING_ON_IMPORT pragma that can be used to encourage people to migrate away from them.

Thoughts?

[gallais]

Thoughts?

Trinary or Ternary?

[JacquesCarette]

Ternary!