Issue #13: Validate redirects

* Add redirects to the common schema

* Initial support for the `items` schema key for validating arrays

* Tests
I got this from [a JSON schema example](http://json-schema.org/example1.html). Looks like `properties` are for objects, but `items` are for arrays.

The "Are all tags strings?" part looks like this:
```
        "tags": {
            "type": "array",
            "items": {
                "type": "string"
            },
            "minItems": 1,
            "uniqueItems": true
        }
```