Canva.Options fields are not exported

[Elliot67]

We currently cannot use the Options struct for the SetOptions() method because its fields aren't exported.

Had to use the helpers function instead :

type OptionsOverride struct {
	Background  color.RGBA
	Foreground  color.RGBA
	LineColor   color.RGBA
	LineWidth   float64
	ColorSchema []color.RGBA
	NIters      int
	Alpha       int
}

func setCanvaOptions(c *generativeart.Canva, options OptionsOverride) {
	c.SetBackground(options.Background)
	c.SetForeground(options.Foreground)
	c.SetLineColor(options.LineColor)
	c.SetLineWidth(options.LineWidth)
	c.SetColorSchema(options.ColorSchema)
	c.SetIterations(options.NIters)
	c.SetAlpha(options.Alpha)
}