Palette can't be modified

[Henrique194]

Say we have a palette with 4 colors. This palette is used by a surface. If I wanted to modify color 1, I would do something like this in C:

SDL_Color color = {0xff, 0xff, 0xff, 0xff};
SDL_SetPaletteColors(surface->format->palette, &color, 1, 1);

In rust bindings we don't have a way to update the color 1, unless we resort to using unsafe rust and mimic the C code:

unsafe {
   let color = SDL_Color {
       r: 0xff,
       g: 0xff,
       b: 0xff,
       a: 0xff,
   };
   let mut colors = vec![color];
   let sdl_surface = *surface.raw();
   let pal = (*sdl_surface.format).palette;
   let colors_ptr = (&mut colors [0]) as *mut SDL_Color;
   
   sys::SDL_SetPaletteColors(pal, colors_ptr, 1, 1);
};

To solve this issue, we may need two new functions: one to retrieve the palette in the Surface struct and other to update the palette based on SDL_SetPaletteColors.
@Cobrand