Release 1.5.0

• Adds config options disable_relationship_getters, custom_sql_identity_function and custom_link_identity to Resource and Repository classes.
• Leveraging custom_sql_identity_function, allows app builders to declare models with composite primary keys that will still work with the auto-generated CRUD routes.
• Adds tests for new functionality.
• Adds .enable_foreignkey_constraints() method to sqlite adapter, to allow effortless enabling of foreign key constraints for sqlite-based applications.
• Reorganizes internal Resource class code to allow proper PK selection when building shadow models (beyond 'id'), and to allow custom_link_identity function to alter Swagger documentation.