in save string, add each layer to a new line. This helps with readability and text manipulation (if we want to edit the save file directly for whatever reason)

fcore/quad-tree.sml

@@ -488,7 +488,7 @@ struct
       val bintree = merge (qtree, grid)
       val coords = BinTree.foldr (toSaveStringFolder, bintree, [])
       val coords = String.concat coords
-      val str = " [ " ^ coords ^ " ] "
+      val str = "\n  [ " ^ coords ^ " ]"
     in
       str :: acc
     end
@@ -498,7 +498,7 @@ struct
       val size = Int.max (canvasWidth, canvasHeight)
       val f = toSaveStringTreeFolder size
 
-      val initial = ["}\n"]
+      val initial = ["\n}\n"]
       val acc = LayerTree.foldr (f, layerTree, initial)
       val acc =
         String.concat