convert

assert(BGR555(31,31,31).convert!RGB888 == RGB888(248, 248, 248));
assert(BGR555(0, 0, 0).convert!RGB888 == RGB888(0, 0, 0));
assert(RGB888(248, 248, 248).convert!BGR555 == BGR555(31,31,31));
assert(RGB888(0, 0, 0).convert!BGR555 == BGR555(0, 0, 0));