Is there a preference for memory order (`C` or `F`) in tabmat?

[mlondschien]

Followup to Quantco/glum#838. In particular, I'd like to avoid any unnecessary copies when creating a

data_continuous = tabmat.DenseMatrix(data[:, continuous_mask], column_names=column_names)

[stanmart]

Tabmat has supports both, so no copies will be made when creating the matrices or doing sandwich and matvec operations. I don't know the performance implications, though. C layout feels more natural for columnar data and matvec, but that's just a hunch.