Fhir-core

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- YAML dump & validate options are added into FHIRAbstractModel.

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- typing hint added for the function ´´create_fhir_type´´ and ´´create_fhir_element_or_resource_type´´.

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- Core configurations for types ``Id`` & ``String`` are coming from constraint module.

- Default maximum char length ``Id`` is now 255.

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- Fixes the function that is checking is_primitive, as missing bytes and bytesarray are added.

- Encoding is handled for Base64Binary type.

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- Fixes extension serialization.

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- Fixes the function that is checking is_primitive.

- Fixes validator for Resource & Element types.