documentation for calc_dragio and formdrag options

[eclare108213]

The current documentation is difficult to find and perhaps confusing. E.g. calc_dragio is listed in the index and case settings, but isn't mentioned in the text where it's used. I initially thought it was a variable-drag formulation, but that doesn't seem to be the case.

The form drag documentation also needs to be reviewed and clarified, if needed.

Is it possible that calc_dragio and formdrag might both be set to .true., and would that be a consistent and meaningful configuration?

[phil-blain]

 The current documentation is difficult to find and perhaps confusing. E.g. calc_dragio is listed in the index and case settings, but isn't mentioned in the text where it's used.

This is addressed in #466.

[phil-blain]

 Is it possible that calc_dragio and formdrag might both be set to .true., and would that be a consistent and meaningful configuration?

I guess it would be possible but it would not change the answers that much I think (compared to just formdrag=.true.). dragio is used to initialize Cdn_ocn in neutral_drag_coeffs, but then it is overwritten if aice > p001. So you get a value of dragio only for these small concentrations.