Fixed #166. Support custom format for slide numbering.

Readme.org

@@ -284,7 +284,18 @@ $ git clone https://github.com/yjwen/org-reveal.git
         ratio.
 
 ** Slide Numbering
-   Activate slide numbers by setting =#+REVEAL_SLIDE_NUMBER:= to =t= (true).
+
+   By default, a flatten slide number is showed at the lower-right corner of each slide.
+
+   To disable slide numbering, please add ~reveal_slide_number:nil~ to
+ ~#+OPTIONS:~ line.
+
+   From Reveal.js 3.1.0, slide numbering can have several custom
+   formats. To choose one format, please set ~reveal_slide_number~ to
+   its proper string. For example, ~reveal_slide_number:h/v~.
+   
+   Supported format string can be found in [[https://github.com/hakimel/reveal.js/#slide-number][Reveal.js manual]].
+   
 
 ** Slide Header/Footer
    Specify Slide header/footer by =#+REVEAL_SLIDE_HEADER:= and

ox-reveal.el

@@ -227,10 +227,10 @@ can contain the following escaping elements:
   :group 'org-export-reveal
   :type 'boolean)
 
-(defcustom org-reveal-slide-number t
+(defcustom org-reveal-slide-number "c"
   "Reveal showing slide numbers."
   :group 'org-export-reveal
-  :type 'boolean)
+  :type 'string)
 
 (defcustom org-reveal-keyboard t
   "Reveal use keyboard navigation."
@@ -591,7 +591,9 @@ overview: %s,
             (if (plist-get info :reveal-progress) "true" "false")
             (if (plist-get info :reveal-history) "true" "false")
             (if (plist-get info :reveal-center) "true" "false")
-            (if (plist-get info :reveal-slide-number) "true" "false")
+            (let ((slide-number (plist-get info :reveal-slide-number)))
+              (if slide-number (format "'%s'" slide-number)
+                "false"))
             (if (plist-get info :reveal-rolling-links) "true" "false")
             (if (plist-get info :reveal-keyboard) "true" "false")
             (if (plist-get info :reveal-overview) "true" "false"))