Allow dichotomous variables in `tbl_continuous()` ?

[ddsjoberg]

There are many tables for analytic results that are the primary result among all subjects on the first line, followed by the same result stratified by another variable. I think allowing a dichotomous variable in tbl_continuous() would help this along.

More generally, adding an overall row to all tables could be useful.... 🤔

[larmarange]

Allowing to add an overall row to all tbl is a good idea.