A new feature function for frequency and univariate summary

[kaigu1990]

I hope this function can sort out some summaries as follows:

• a frequency summary, like what's the count of male and female and corresponding percentage in each group.
• a univariate summary, like what's the mean, median and range of age variable.
• Export this summary table in PDF.

We can see that most tables in clinical trial reports can be categorized to frequency or univariate tables. For example, demographic and disposition tables belong to the frequency table, and statistical and lab summary tables belong to the univariate table.

Update:
This section can refer to cards package metioned in R-pharam 2024 conference.
https://www.danieldsjoberg.com/ARD-RinPharma-workshop-2024/slides/01-intro-cards/#/cards-ard_continuous-fmt_fn