SDL : Comments fixed and added in SDLDisplay class

signed-off-by: Geoffrey Hecht  <geoffrey.hecht@gmail.com>
SDL : Comments fixed and added in SDLDrawable class

signed-off-by: Geoffrey Hecht  <geoffrey.hecht@gmail.com>
SDL : Comments fixed and added in SDLImage class

signed-off-by: Geoffrey Hecht  <geoffrey.hecht@gmail.com>