Reformatting: Lay out _list() file numbering in multi-line.

...like the following complex formatting and filtering steps.

todo.sh

@@ -775,7 +775,11 @@ _list() {
     fi
     items=$(
         sed = "$src"                                            \
-        | sed "N; s/^/     /; s/ *\(.\{$PADDING,\}\)\n/\1 /"    \
+        | sed '''
+            N
+            s/^/     /
+            s/ *\([ 0-9]\{'"$PADDING"',\}\)\n/\1 /
+	  '''                                                 \
         | grep -v "^[ 0-9]\+ *$"
     )
     if [ "${filter_command}" ]; then