add a Page#markup_class reader

lib/gollum/page.rb

@@ -168,7 +168,7 @@ module Gollum
     #
     # Returns the String data.
     def formatted_data(&block)
-      @blob && @wiki.markup_classes[format].new(self).render(historical?, &block)
+      @blob && markup_class.render(historical?, &block)
     end
 
     # Public: The format of the page.
@@ -180,6 +180,13 @@ module Gollum
       self.class.format_for(@blob.name)
     end
 
+    # Gets the Gollum::Markup instance that will render this page's content.
+    #
+    # Returns a Gollum::Markup instance.
+    def markup_class
+      @markup_class ||= @wiki.markup_classes[format].new(self)
+    end
+
     # Public: The current version of the page.
     #
     # Returns the Grit::Commit.