Add an option which combines --prefer and "link"

[ssokolow]

Once issues #5 and #7 are resolved, I'll want to add a command line switch with a name like --autolink or --link-if which is used similarly to --prefer.

The purpose would be to allow behaviours like "If you see a group of duplicates and one is named Folder.jpg or AlbumArtSmall.jpg, then hardlink them all together without asking."

I'll still need to finish the design work on it though.