Allow users to pass their own summary functions to codebook

[mbcann01]

Overview

I think it would be cool if users could eventually add their own summary functions to codebook(). The defaults could look something like this, perhaps:

codebook(
  df,
  title = NA,
  subtitle = NA,
  description = NA,
  keep_blank_attributes = FALSE,
  no_summary_stats = NULL,
  digits = 2,
  # This is the part where users can enter their own summary stat functions
  # Will also need to include flextable formatting functions.
  summary_stats_fns = list(
    numeric = cb_summary_stats_numeric(),
    many_cats = cb_summary_stats_many_cats(),
    few_cats = cb_summary_stats_few_cats(),
    time = cb_summary_stats_time()
  )
)

Task list

• [ ] Get this working
• [ ] Probably create a vignette about how to do adjust summary stats functions. Can also be used for exploratory descriptive analysis.