This breaks the API of GameBoyAdvanvce::save_state and restore_state methods.
Currently as WIP only SDL2 frontend will adjust.
Former-commit-id: 1df15c8697fef0f6adddb07a6d653947c622ba12
Former-commit-id: 2ea339dc6a0d1e7539d167c4df29694b408303da
Serde doesn't like Rc that much :(
Fixes#142
Former-commit-id: e1e8a96b4867e351d103fb7d92d71b0434e8fc31
Former-commit-id: 28366bbb36b3e93b574f397b103a483844fd8131