Add init methods to UIColor

[zakkhoyt]

Add init methods which accept our tuples RGB, HSB, CMYK

[zakkhoyt]

I added the following class factory methods

    public class func colorWith(hexString: String, alpha: CGFloat = 1.0) -> UIColor 

    public class func colorWith(rgb: RGB, alpha: CGFloat = 1.0) -> UIColor 

    public class func colorWith(hsb: HSB, alpha: CGFloat = 1.0) -> UIColor 

    public class func colorWith(cmyk: CMYK, alpha: CGFloat = 1.0) -> UIColor 

and the following inits

    public convenience init(rgb: RGB, alpha: CGFloat = 1.0) 
    public convenience init(hsb: HSB, alpha: CGFloat = 1.0) 
    public convenience init(cmyk: CMYK, alpha: CGFloat = 1.0) 

as well as adding an optional alpha parameter to

public convenience init(hexString:String, alpha: CGFloat = 1.0) {