Cleanup CEvent
	Make it into a proper class with a ctor and use ctor instead of {}
	Put the focus event boolean into .key instead of .x (why was it there?)
	Make a standard named ctor for packing a uint64_t into an event and,
	Make named ctors for Ping, Command, and UIChanged events, using it.
	Rename UIChange to UIChanged, clarifying that it is a notification.
	Yes, this breaks the API and ABI. For the better.