SdFat v2 compatibility

[awickert]

On first glance, the lack of compatibility may stem from some directory-related commands, but not sure yet.

We could update to work with SdFat v2 (the best solution) and/or update https://github.com/NorthernWidget/NorthernWidget-libraries to include the most recent SdFat v1.

I am guessing that this issue will also affect https://github.com/NorthernWidget-Skunkworks/Resnik_Library.

[awickert]

We should also add some documentation to this effect for the time that this will not be resolved, and/or perhaps change https://github.com/NorthernWidget/Firmware-Aggregator and/or https://github.com/NorthernWidget/NorthernWidget-libraries to reflect this -- more likely a manual change to the latter.