Openapi-type

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* ``ContentTypeFormat`` is redefined as a new type of ``str`` (used to be a strict Enum)
for allowing non-common yet valid type representations.

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* Support for ``/components/responses``
* Support for ``/components/headers``
* Support for ``/components/parameters``
* ``ObjectWithAdditionalProperties`` supports boolean value
* Support for header schemas referenced through ``$ref``

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* Support for Content Media Type with charset.

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* Attributes use pythonic ``snake_case``.

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* Initial Release