Internal: Convert value between dimension units
unitConverter(value = NA, fromunit = NA, tounit = NA, dpi = NA)
A numeric value or numeric vector to convert
A character indicating the current unit of the value. Options are "cm", "mm", "in" or "px".
A character indicating the unit to change to. Options are "cm", "mm", "in" or "px".
A numeric indicating the resolution for pixel conversion. This should be in PPI (pixels per inch).
Returns a numeric value or numeric vector in changed units.