RawRepresentable, meet NSCoding

RawRepresentableExtensions.swift

extension RawRepresentable where Self: NSCoding {
    init?(rawValue: NSData) {
        if let instance = NSKeyedUnarchiver.unarchiveObjectWithData(rawValue) as? Self {
            self = instance
        } else {
            return nil
        }
    }
    
    var rawValue: NSData {
        get {
            return NSKeyedArchiver.archivedDataWithRootObject(self)
        }
    }
}