v0.10.0.beta3 - `apply_join` for relationships, caching performance

Adds the following:

• relationships can now have an apply_join callable to allow customization of how the relationship is joined to the parent table.
• cache reads and writes are batched, where supported by rails (5.2 and up). This results in many few calls to the cache.
• A rake task, jsonapi:resources:check_upgrade, to help with upgrading from earlier versions.