* Switched event type to enum (int32)
* Switched polling by mask to polling by type range
* Added SDL_RegisterEvents() to allow dynamic user event registration
* Spread events out to allow inserting new related events without breaking binary compatibility
* Added padding to event structures so they're the same size regardless of 32-bit compiler structure packing settings
* Split SDL_HasEvent() to SDL_HasEvent() for a single event and SDL_HasEvents() for a range of events
* Added SDL_GetEventState() as a shortcut for SDL_EventState(X, SDL_QUERY)
* Added SDL_FlushEvent() and SDL_FlushEvents() to clear events from the event queue
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