new function: andThenAttempt

Like `andThen`, but it can fall back to the original value if the function fails.

```
andThenAttempt : (a -> Maybe a) -> Maybe a -> Maybe a
andThenAttempt f a =
    a
        |> Maybe.andThen f
        |> orElse a
```

This would require some investigation to see if it's a common enough use case to include. If you would use this in your projects, comment with your use case.