Unify returning of Accept-Post and Accept-Patch items.

Use resource allowed patches in OPTIONS.

Include basic description of the error and the steps to resolve them.

Implement default error handler, unify error handling logic in server.

Dynamic attributes for metadata are included for createdAt and updatedAt.

Include example project and requests.

Tidy up some parts of the codebase.

Genericize data used for data source tests.

Check result data in tests.

Include data source tests for query and initialization.

Put data source to its own package.

Prepare project for multiple packages.