#275 Allow several "--print-column" for "--list"

[Simón]

I have a list with 2 values:

yad --list --column=Descargar:CHK --column=Label --column=File --checklist ...

And I want only print columns 2 and 3 of selected rows. But with actual configuration only I can select one column or all. The first column is useless, it's always TRUE.