Add Swift gradient output

[larsenwork]

Similar to copy CSS - should be easy: https://stackoverflow.com/a/33800041

[hanawat]

Thanks for the great plugin.
This is snippets for use with Swift from the output CSS.

/* Gradient direction goes here */
hsl(272,29.64%,49.61%) 0%,
hsl(271.41,29.91%,49.28%) 0.05%,
hsl(269.78,30.69%,48.37%) 0.36%,
...

let layer = CAGradientLayer()
layer.colors = [
    .init(hue: 272.00, saturation: 0.2964, lightness: 0.4961),
    .init(hue: 271.41, saturation: 0.2991, lightness: 0.4928),
    .init(hue: 269.78, saturation: 0.3069, lightness: 0.4837),
    ...
]
layer.locations = [
    0.0000,
    0.0005,
    0.0036,
    ...
]

extension UIColor {
    convenience init(hue: CGFloat, saturation: CGFloat, lightness: CGFloat, alpha: CGFloat = 1.0) {
        precondition(.zero...360.0 ~= hue, "Input hue is out of range 0 to 360")
        precondition(.zero...1.0 ~= saturation, "Input saturation is out of range 0 to 1")
        precondition(.zero...1.0 ~= lightness, "Input lightness is out of range 0 to 1")
        precondition(.zero...1.0 ~= alpha, "Input alpha is out of range 0 to 1")
        let brightness = lightness + saturation * min(lightness, 1.0 - lightness)
        let saturation = brightness.isZero ? .zero : 2.0 * (1.0 - lightness / brightness)
        self.init(hue: hue / 360.0, saturation: saturation, brightness: brightness, alpha: alpha)
    }
}