sed: Support substitution of \t, \n.

gash/commands/sed.scm

@@ -44,6 +44,15 @@
                    (char-numeric? (cadr lst)))
               (let ((i (- (char->integer (cadr lst)) (char->integer #\0))))
                 (append (string->list (match:substring m i)) (loop (cddr lst)))))
+             ((and (eq? (car lst) #\\)
+                   (eq? (cadr lst) #\n))
+              (append '(#\newline) (cddr lst)))
+             ((and (eq? (car lst) #\\)
+                   (eq? (cadr lst) #\t))
+              (append '(#\tab) (cddr lst)))
+             ((and (eq? (car lst) #\\)
+                   (eq? (cadr lst) #\r))
+              (append '(#\return) (cddr lst)))
              ((and (eq? (car lst) #\\)
                    (eq? (cadr lst) #\\))
               (append '(#\\ #\\) (cddr lst)))