Add support for $ref in status code responses

[amanda-mitchell]

According to the spec for Fixed Fields and Patterned Fields of the Responses Object, it is permissible to use a $ref object to describe API responses.

Currently, attempting to parse an Open API definition that uses this feature yields an OpenApiError indicating that "$ref is not a valid property at {path}".

[darrelmiller]

Thanks. Will get that fixed ASAP.

[darrelmiller]

This is fixed in build #31 and should be in Nuget release 0.8.0