Add support for deprecated attribute

[wilsonge]

Add support for the deprecated operation tag (Documented at: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#fixed-fields-5)

[nknapp]

Yes, that would be cool. Could you submit a PR?

This should probably be added here and here

And a test that ensures, that it is there, would be cool too.