Return user response in callback

Great plugin. I'm still pretty new to gulp so forgive me if this doesn't make any sense, but should the user input be returned to the callback? That way you could do something like this:

```
.pipe(prompt.input(message, (val) ->

  switch val.value
    when 'a'
      type = 'patch'
    when 'b'
      type = 'minor'
    when 'c'
      type = 'major'
```