Convert stat box groups output to list of data frames

Convert stat box groups output to list of data frames for reuse in other contexts, typically in reports generated by rmarkdown and knitr.

sbg_to_tables(d, grp, rnd = 0)

Arguments

d	data frame to use for generating stat box groups.
grp	character or `NULL`, factor variable (column name) in `d` used to determine the number of groups of stat box sets.
rnd	numeric, number of decimal places to round values to.

a list of data frames.

#not run