Album art support #10

There are different image backends for terminals, like sixel, jp2a etc.

ditty could have a second column with a thumbnail, like here

I know this is quite low-priority and difficult task but if you have a wish to do it here's a sixel lib

Thanks, I'll share an update when I have a chance to experiment with this.

changed title from {-Songs thumbnails-} to {+Album art support+}