Models and their properties are flat hashes, *not* arrays of hashes

This change corrects the generated JSON spec for the `models` section in an API declaration.
With this, the "Data Type" column in the Swagger UI also correctly shows information about model parameters.

See:
![image](https://cloud.githubusercontent.com/assets/569413/3728755/d30e18d2-16af-11e4-9f02-afef58f36010.png)