Make it easier to get *total* population N ?

[bzkrouse]

This can definitely be inferred from the ard_* results but requires post processing that users will have to do each time. For example, ard_categorical(ADSL, variables = TRTA) gives treatment group-level n's and population Ns. For downstream use, they would need to either manipulate the rows with Ns (keeping just 1 row and renaming it to be clear it is a total N), or do some other manipulation.

In ard_stack() with .overall = TRUE we get population-level stats for all the variables, so this would go well with those rows.