* add hash benchmarking to performance tests
* Add missing attribute in README example
* Disable GC before doing performance test
* Enable oj to AM for fair benchmark test
* Support for polymorphic associations
* Optional dictionary for polymorphic associations
* Added polymorphic record types memoization
* Updated performance tests for polymorphic examples to include jsonapi-rb
* Allow has_one nil association
* add test for when has_one returns nil
* modify has_one extension method, add active record test
* Use try operator to support old rubies
