Creates a single file upload field.

![TodayCMS File](http://space.todaymade.com/todaycms/file.jpg)

    "file": {
        "title": "File Field",
        "type": "file"
    }

Returns an array.

    [file] => Array
        (
            [caption] =>
            [date] => 11/1/2012
            [url] => http://todaycms.s3.amazonaws.com/...filename.pdf
            [name] => filename.pdf
        )