Add HSP colors to rgb_color

[nephele]

rgb_color should obtain an API to set it's brightness in addition to how it is now received.

This would require to internally convert to HSP, adopt the passed in Brightness, and convert back to rgb.

example api: rgb_color::SetBrightness(float brightness) (0-1) HSP system: ​http://alienryderflex.com/hsp.html

Example problem (With current HSL api):

hsl_color normalViewColor = hsl_color::from_rgb(viewColor);
rgb_color failureColor = ui_color(B_FAILURE_COLOR);
hsl_color newViewColor = hsl_color::from_rgb(failureColor);
if (normalViewColor.lightness < 0.15)
    newViewColor.lightness = 0.15;
else if (normalViewColor.lightness > 0.95)
    newViewColor.lightness = 0.95;
else
    newViewColor.lightness = normalViewColor.lightness;
 
    viewColor = newViewColor.to_rgb();

New api:

rgb_color failureColor = ui_color(B_FAILURE_COLOR);
if (viewColor.Brigthness() < 0.15)
    failureColor.SetBrightness(0.15);
else if (viewColor.Brigthness() > 0.95)
    failureColor.SetBrightness(0.95);
else
    failureColor.SetBrightness(viewColor.Brigthness());

viewColor = failureColor;

Example api with clamp values:

rgb_color failureColor = ui_color(B_FAILURE_COLOR);
failureColor.SetBrightness(viewColor.Brigthness(), 0.15, 0.95);
viewColor = failureColor;