Ddbcereal

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* Faster Binary (de)serialization in raw transport mode.
* Fix main constructor strict type checking for referring projects.
* Expose `ddbcereal.FLOAT_ONLY`

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* Empty Python set is now serialized to a configurable Set type.
* Faster serialization for Number Sets and Binary Sets.
* Behind the scenes, DynamoDBType enumerations are now ``str``\ s of
their type symbol.

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* Fix exceptions from typing on pre-3.9 Python

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* Remove ``nullify_empty_string`` and ``validate_strings`` options. DynamoDB
supports empty strings now and users could do this at a different layer.
* Fix :py:meth:`ddbcereal.Serialize.serialize_item`.
* Fixed typing issues.
* Publish exceptions.

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First release, feature parity with boto3 [de]serializers.