Unsupported Support

This fix makes types that are not yet supported by OpenAPIKit (see the Specification Coverage) ignored silently instead of letting them cause decoding to fail.

The idea is, it's better to still be able to parse documentation even if not all of it has OpenAPIKit representation yet. OpenAPIKit is really close to supporting all OpenAPI types but not quite there yet. At least now the existence of those types in a document won't render the document invalid in the eyes of OpenAPIKit.