4.1 comes with a more granular data definition hierarchy that will make it easier to
write more API definitions. This marked by the introduction of a new member known
as Entity. Entity only needs a pk() and get key(), as well
as member declarations to integrate fully.
Entity
- Useful for nested entities that don't have endpoints like LatestPrice.
- Useful for non-REST style APIs like GraphQL.
- Simplifies defining nested entities.
