Support "models" Swagger feature

[singalen]

Like, you know,

    "Pet": {
        "id": "Pet",
        "required": [
            "id",
            "name"
        ],
        "properties": {
            "id": {
                "type": "integer",
                "format": "int64",
                "description": "Unique identifier for the Pet",
                "minimum": "0.0",
                "maximum": "100.0"
            },
            "category": {
                "$ref": "Category",
                "description": "Category the pet is in"
            },
            "name": {
                "type": "string",
                "description": "Friendly name of the pet"
            }
    }

[singalen]

I'm doing some stuff in my repo, I believe it is useful... though not too clean.
Is it OK for a pull request?