Indicate if a parameter requires a reference column

[billdenney]

For any secondary parameters (e.g. clr, metabolic ratio, relative bioavailability, etc.), add an argument to add.interval.col() indicating reference_required = TRUE. The default is reference_required = FALSE.

This modification will occur here:

pknca/R/001-add.interval.col.R

Line 82 in e241322

add.interval.col <- function(name,

Related to #76