Better debug impls

Some whiskers have internal values which only really make sense if you are familiar with the CATS standard. For example:

        Gps {
            latitude: 506432319,
            longitude: 1317180968,
            altitude: 0.0,
            max_error: 12,
            heading: 0,
            speed: 0.0,
        },

The latitude and longitude look like nonsense since we encode them as 32-bit integers. If we implement Debug ourselves we could make this look far more sensible by converting the lat/lon to floats in the usual range.