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Refactored fetching resource collections:
- SQL query optimizations for 'include' and 'relationship' objects, using `selectinload`
(3x-5x performance improvement when tested on large datasets)
- New parameter 'include_links' which controls should relationship objects include links. They are not required by
JSON API, and disabling them significantly improves performance
- New interfaces for Serializer and Deserializer classes.
- APIManager requires Serializer/Deserializer objects instead of functions for `serializer`/`deserializer` options
Deprecations:
- 'single' parameter is no longer supported - makes code complicated, is not defined in JSON API specs and can be easily
replicated on a client side
- 'group' parameter is not longer supported - not defined in JSON API specifications, confusing and broken for PostrgeSQL
- JSONP callbacks are no longer supported - please reach out if you have a use case for them