html: Add sxml->html-string.

* haunt/build/html.scm (sxml->html-string): New procedure.

haunt/build/html.scm

@@ -28,7 +28,8 @@
   #:use-module (ice-9 match)
   #:use-module (ice-9 format)
   #:use-module (ice-9 hash-table)
-  #:export (sxml->html))
+  #:export (sxml->html
+            sxml->html-string))
 
 (define %void-elements
   '(area
@@ -368,3 +369,9 @@ list ATTRS and the child nodes in BODY."
      (string->escaped-html text port))
     ;; Render arbitrary Scheme objects, too.
     (obj (object->escaped-html obj port))))
+
+(define (sxml->html-string sxml)
+  "Render SXML as an HTML string."
+  (call-with-output-string
+   (lambda (port)
+     (sxml->html sxml port))))