Add ability to document API operations that support multiple content type responses
- relevant 'supportedContentTypes' field will be renamed to 'produces' in 1.2 spec (release not imminent)
- default behaviour if no 'produces' specified is to return 'application/json' as this is current behaviour of swagger-ui
Merge pull request #272 from caoilte/2.2.x_2.9

Add ability to document API operations that support multiple content type responses