Pass multiple columns to marbl%set_interior_forcing

[mnlevy1981]

Right now we can pass multiple columns to marbl%set_surface_forcing(), but marbl%set_interior_forcing has to be called one column at a time. It would likely be a huge performance gain if we could pass in multiple columns.

This would supercede #66, but that ticket raises a good point about how this assumption that num_elements_interior_forcing is assumed to be 1 at some points in the code.

[mnlevy1981]

No clear consensus on whether this would actually be a performance gain... so this is being put on the back-burner to be revisited later.

[mnlevy1981]

A lot of the MARBL code has a placeholder dimension for the column id -- currently this is the first dimension in the array, but is that where we want it? As written, we might be getting un-necessary memory copies.