Checks the event queue for messages and optionally returns them.
If action is SDL_ADDEVENT, up to numevents events will be added to the back of the event queue.
If action is SDL_PEEKEVENT, up to numevents events at the front of the event queue, matching mask, will be returned and will not be removed from the queue.
If action is SDL_GETEVENT, up to numevents events at the front of the event queue, matching mask, will be returned and will be removed from the queue.
The mask parameter is an bitwise OR of SDL_EVENTMASK(event_type), for all event types you are interested in.
This function is thread-safe.