Make multi-disc albums to create separate directories

When moving files to the Music Library directory, if the album has
multiple discs, inside the album folder separate tracks inside the
corresponding disc directory and re-number the tracks per disc.

beets/config.yaml

@@ -1,10 +1,16 @@
 sort_item: albumartist+ album+ disc+ track+
 format_item: $track.$title - $artist ($album)
+per_disc_numbering: yes
 
 paths:
-    default: $albumartist/$album%aunique{}/$track.$title
+    default: $albumartist/$album%aunique{}/%if{$multidisc,Disc $disc/}$track.$title
     comp: $albumartist/$album%aunique{}/$track.$title
 
 import:
     write: no
     copy: no
+
+plugins: inline
+
+item_fields:
+    multidisc: True if disctotal > 1 else False