Adapter to make Argo JSON parsing library works with Opera

ArgoAdapterForOpera.swift

extension Argo.Decodable where Self.DecodedType == Self, Self: OperaDecodable {
    static func decode(json: AnyObject) throws -> Self {
        let decoded = decode(JSON.parse(json))
        switch decoded {
        case .Success(let value):
            return value
        case .Failure(let error):
            throw error
        }
    }
}

extension NSDate: Decodable {
    public typealias DecodedType = NSDate
    
    public class func decode(j: JSON) -> Decoded<NSDate> {
        switch j {
        case .String(let dateString):
            return  dateString.toDate(DateFormat.ISO8601Format(.Full)).map(pure) ?? .typeMismatch("NSDate", actual: j)
        default: return .typeMismatch("NSDate", actual: j)
        }
    }
}

extension NSURL: Decodable {
    public typealias DecodedType = NSURL
    
    public class func decode(j: JSON) -> Decoded<NSURL> {
        switch j {
        case .String(let urlString):
            return NSURL(string: String(urlString)).map(pure) ?? .typeMismatch("URL", actual: j)
        default: return .typeMismatch("URL", actual: j)
        }
    }
}