Multiple Callbacks section missing to define the other two callback events

[MathanprasathK]

I am referring this url - https://swagger.io/docs/specification/callbacks/, where the section called Multiple Callbacks suppose to define 3 callback events but it currently defined just one call back event named - inProgress: and used all the three callback messages underneath this event.

I suppose the documentation should be updated to show example defining other two events namely failed: & success: and define the callback messages accordingly.

[sskipstress]

Duplicate of #263