SDL_Surface has been simplified and internal details are no longer in the public structure.
The `format` member of SDL_Surface is now an enumerated pixel format value. You can get the full details of the pixel format by calling `SDL_GetPixelFormatDetails(surface->format)`. You can get the palette associated with the surface by calling SDL_GetSurfacePalette(). You can get the clip rectangle by calling SDL_GetSurfaceClipRect().
SDL_PixelFormat has been renamed SDL_PixelFormatDetails and just describes the pixel format, it does not include a palette for indexed pixel types.
SDL_PixelFormatEnum has been renamed SDL_PixelFormat and is used instead of Uint32 for API functions that refer to pixel format by enumerated value.
SDL_MapRGB(), SDL_MapRGBA(), SDL_GetRGB(), and SDL_GetRGBA() take an optional palette parameter for indexed color lookups.
This does something a little weird, in that it doesn't care what
`__ANDROID_API__` is set to, but will attempt to dlopen the system
libraries, like we do for many other platform-specific pieces of SDL.
This allows us to a) not bump the minimum required Android version, which is
extremely ancient but otherwise still working, doing the right thing on old
and new hardware in the field, and b) not require the app to link against
more libraries than it previously did before the feature was available.
The downside is that it's a little messy, but it's okay for now, I think.
