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Improvements
- Issue5: Now ``ElasticsearchEngine::get_index_name`` takes one optional parameter ``resource_type``.
- Add supports for python version 3.6.
Breaking
- Make full capability with `fhir.resources <https://pypi.org/project/fhir.resources/>`_ version ``6.x.x``,
please have a look of revolutionary changes of ``fhir.resources``.