Replaced key paths by fetchable members

Changed

• Moved away from KeyPaths to user FetchableMembers specified for each entity, using a macro or manually.
• Predicate writing has changed to use fetchable members, which feels more natural in Swift, and restrict fetching ton only available members
• FetchableManagedObject macro to conform to Fetchable and add fetchable members.

Warning

This is a breaking change.

This version will most likely evolve into a stable 1.0.0 release.