Add support for separator columns.

src/listing.scm

@@ -141,14 +141,15 @@
 	   #:highlight-pre (hl-pre a:error)
 	   #:highlight-post (hl-post a:default)
 	   #:context (context 3)
-	   #:keys (keys '(number line comment)))
+	   #:keys (keys '(number -- line -- comment)))
    (let loop ((lines lines)
 	      (number 1)
 	      (printed-something #f)
 	      (was-printing #f)
 	      (rtbl '()))
      (if (null? lines)
-	 (print (table->string (reverse rtbl)))
+	 (print (table->string (reverse rtbl)
+			       ))
 	 (let* ((highlight (match-highlight number highlights))
 		(hl-type (if highlight (cadddr highlight) #f))
 		(hl-def (assq hl-type highlight-rules))
@@ -198,6 +199,8 @@
 						   comment
 						   post-str)
 					   ""))
+				      ((--)
+				       "\xc2\xa0")
 				      (else
 				       (format "~A~A ~A"
 					       pre-str