Allows to change brightness of an UIColor.

UIColor+Brightness.swift

private extension UIColor {
    func addedBrightness(value: CGFloat) -> UIColor {
        var cs: (hue: CGFloat, saturation: CGFloat, brightness: CGFloat, alpha: CGFloat) = (0.0, 0.0, 0.0, 0.0)
        self.getHue(&cs.hue, saturation: &cs.saturation, brightness: &cs.brightness, alpha: &cs.alpha)
        return UIColor(hue: cs.hue, saturation: cs.saturation, brightness: cs.brightness + value, alpha: cs.alpha)
    }
}