`wait_*_event() -> Event` functions should return Result instead of Option

[phip1611]

It might be better to return Result rather than Option for wait_for_packet. I don't see a normal good case where it is okay to return None when we expect an event to be returned from that function.

This applies at least to:

• wait_for_packet
• wait_for_key_event
• wait_for_input_event

Please investigate the usefullness before starting to implement.