Gets the info from a UIKeyboardWill(Show/Hide)Notification and returns it in a not-terrible tuple

keyboardInfoFromNotification.swift

public func keyboardInfoFromUserInfo(userInfo: [NSObject: AnyObject]) -> (beginFrame: CGRect, endFrame: CGRect, animationCurve: UIViewAnimationOptions, animationDuration: Double)? {
    if let beginFrameValue = userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue,
        let endFrameValue = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
        let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? NSNumber,
        let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? NSNumber {
            return (
                beginFrame:         beginFrameValue.CGRectValue(),
                endFrame:           endFrameValue.CGRectValue(),
                animationCurve:     UIViewAnimationOptions(rawValue: animationCurve.unsignedIntegerValue << 16),
                animationDuration:  animationDuration.doubleValue)
    }
    return nil
}