Add tbl_ard_summary(overall) argument?

[ddsjoberg]

Adding an overall column to a demographics table is super common.

The cards package makes it simple to add overall statistics in the ard_stack() function. Since we'll already have all the statistics grouped together in a single ARD, it would be easiest to simply request the overall column in tbl_ard_summary(), which in turn would run add_overall.tbl_ard_summary()