Add a feature to split large data frame

[atusy]

Something like

cols

mtcars %>%
  split_cols(3) %>% # returns `list_of_data_frame` class
  as_flextable() # works as lapply(x, as_flextable)

if df is grouped, show grouping variables for each flextable.

rows

mtcars %>%
  splot_rows(3) %>% # returns `list_of_data_frame` class
  as_flextable() # works as lapply(x, as_flextable)