TODO: Fix events

[Lucretia]

This is two issues in one:

• [ ] Need a tagged event hierarchy rather than a copy of the C struct.
  • [ ] Root type
  • [ ] Keyboard type
  • [ ] Joystick type
  • [ ] Mouse type
• [ ] Rename SDL.Events.Events and make it a private package, or move the Events type to the private part of SDL.Events.
• [ ] Move SDL.Events.Events.Poll to SDL.Events.Poll and change to use the tagged types.
  • [ ] Use Ada's factory for creating tagged types - too much overhead, too slow?
• [ ] Investigate calling SDL.Events.Poll in the library, copying all events to an event queue held in a protected object. This would help with tasking at a higher level. This might also be a bit slower, needs to be checked.