Added Math::Round to dependency list in Makefile.PL. Credit - Syohei YOSHIDA.
        Refactored methods to return N/A first before any further proessing is done
        Cleaned up unit tests
        get_disk_model() only outputs just the model information now.
        Added get_disk_errors()
        Methods now validate the device passed to it, to ensure smartctl has already read it
        Added unit tests to test passing invalid device to methods
        Changed to croak() as I didn't feel a trace was necessary with proper error returning.