/*
 * Apply an Imlib2::ColorModifier to the image
 *
 * Examples:
 *   # modify the contrast of the entire image
 *   cmod = Imlib2::ColorModifier.new
 *   cmod.contrast = 1.5
 *   image.apply_cmod color_mod
 *
 *   # adjust the gamma of the given rect
 *   cmod = Imlib2::ColorModifier.new
 *   cmod.gamma = 0.5
 *   rect = [10, 10, 20, 40]
 *   image.apply_color_modifier cmod, rect
 *
 */
static VALUE image_apply_cmod(int argc, VALUE *argv, VALUE self) {