Use SDL_PIXELFORMAT_RGB565, which is the most common 16-bit format

docs/README-migration.md

@@ -200,8 +200,7 @@ But if you're migrating your code which uses masks, you probably have a format i
 0x00FF0000 0x0000FF00 0x000000FF 0xFF000000 => SDL_PIXELFORMAT_ARGB8888
 0x0000FF00 0x00FF0000 0xFF000000 0x000000FF => SDL_PIXELFORMAT_BGRA8888
 0x000000FF 0x0000FF00 0x00FF0000 0xFF000000 => SDL_PIXELFORMAT_ABGR8888
-0x00007C00 0x000003E0 0x0000001F 0x00000000 => SDL_PIXELFORMAT_RGB555
-0x00007C00 0x000003E0 0x0000001F 0x00008000 => SDL_PIXELFORMAT_ARGB1555
+0x0000F800 0x000007E0 0x0000001F 0x00000000 => SDL_PIXELFORMAT_RGB565
 ```