add inverse color logic using 'inv' url param

// - if the URL has a background and/or a foreground defined by usign parameters 'bg' and 'fg'

//     we return those.

//   e.g: some/url?bg=FFFFFF&fg=222222

// - if you use parameter 'inv' you can invert the colors.

//   This is true only if the number of colors is equal to 2 and you use 'theme' colors or default ones.

//   e.g: some/url?inv=1

//        some/url?theme=frogideas&numcolors=2&inv=1

func Colors(r *http.Request) (colors []color.RGBA) {

	if newColors, err := UserColors(r); err == nil {

			colors = append(colors, m["base"]...)

		}

	}

	return colors

	if len(colors) == 2 {

		if Inverse(r) {

			tmp := colors[0]

			colors[0] = colors[1]

			colors[1] = tmp

		}

	}

	return

}

// GColors returns an array of colors based on a HTTP request.

	return bg, fg

}

// UserColors extract an array of hexadecimal colors and returns an array of color.RGBA

// UserColors extract an array of hexadecimal colors from an HTTP request

// and returns an array of color.RGBA

func UserColors(req *http.Request) ([]color.RGBA, error) {

	if err := req.ParseForm(); err != nil {

		return []color.RGBA{}, fmt.Errorf("colors: unable to parse form")