Rewrite vcard function using format

tsv2vcard.scm

@@ -16,19 +16,7 @@
            (else (iter len rem (+ idx 1) res))))))
 
 (define (vcard name number)
-  (with-output-to-string
-    (lambda ()
-      (display "BEGIN:VCARD")
-      (newline)
-      (display "N:;")
-      (display name)
-      (display ";;;")
-      (newline)
-      (display "TEL;TYPE=cell:")
-      (display number)
-      (newline)
-      (display "END:VCARD")
-      (newline))))
+  (format "BEGIN:VCARD~%N:;~a;;;~%TEL;TYPE=cell:~a~%END:VCARD~%" name number))
 
 (define (tsv-contact->vcard line)
   (let* ((fields (tsv-fields line))