Hi,
This may be a pretty simple (and not particularly embedded-related) question: I have a struct that is generic over `embedded_hal::spi::SpiDevice` and `embedded_hal::digital::InputPin`. Both of these traits also imlement a trait `ErrorType`, but they are not related.
What would be the best way to return one or the other error?
My first thought was something like: 

```
pub enum ErrorKind<S, P> where S: SpiDevice, P: InputPin{
    SpiError(S::Error),
    PinError(P::Error),
    Other,
}
```
but that makes it impossible to implement `From<>`