ability to link all files in a single dir and specify multiple --d as destination with --link

[Jonathan Kirszling]

I want to sort my pictures as phockup/YYYY/MM, but I would also like to get a phockup/all directory.
It would be great to :

• improve -d to be able to add strings, and specify date part in gnu-date format like -d +%Y/%m for YYYY/MM, or simply -d all
• be able to specify mutliple -d with --link

# from
$ phockup  ~/img/photos ~/img/phockup/year-month -d YYYY/MM --link --progress --original-names
$ cd ~/img/phockup
$ find year-month/ -type f -exec ln {} all \;

# to
$ phockup  ~/img/photos ~/img/phockup -d "+year-month/%Y/%m" -d "all" --link --progress --original-names