Set default values for parameter keys and add more info to swagger doc

With this change, the keys for the parameters, filters, etc. are created directly in the class `ApiDoc` when reading the annotations, so we can rely on them in the formatters. I'm not 100% sure if this is the correct way and am happy to get some feedback.

I also added some more information to the output of the `SwaggerFormatter` like descriptions, min/max values and data types.