This crate provides tools for using SDL 3's main and callback APIs.
To provide your own main but call it through SDL, use the [main] attribute macro.
See the documentation for that for more information.
To use the SDL callback API, you can use either the [app_impl] attribute macro,
or all four of the [app_init], [app_iterate], [app_event] and [app_quit]
attribute macros. Don't use the main attribute macro in this mode.
See the documentation for more information.