adorn_ns - add big.mark for large numbers (1,000 vs 1000 OR 1B vs 1000000000)

[Chanelle280]

Feature requests

The feature would make adding a big.format to large numbers much easier.

Brief description of the problem

I'm trying to add a comma to large number but I'm very confused as to how to do this.

adorn_totals(where = "row") %>%
adorn_percentages("col") %>%
adorn_pct_formatting(digits = 1) %>%
adorn_ns(position = "front", big.format = ",")

[sfirke]

Will be addressed in #444