Add custom date format %o for ordinal representation of the day

_config.yml

@@ -11,6 +11,7 @@ simple_search: http://google.com/search
 # Default date format is "ordinal" (resulting in "July 22nd 2007")
 # You can customize the format as defined in
 # http://www.ruby-doc.org/core-1.9.2/Time.html#method-i-strftime
+# Additionally, %o will give you the ordinal representation of the day
 date_format: "ordinal"
 
 # RSS / Email (optional) subscription links (change if using something like Feedburner)
@@ -92,6 +93,6 @@ disqus_show_comment_count: false
 
 # Google Analytics
 google_analytics_tracking_id:
-   
+
 # Facebook Like
-facebook_like: true   
+facebook_like: true

plugins/date.rb

@@ -29,12 +29,16 @@ module Octopress
       end
     end
 
+    # Formats date either as ordinal or by given date format
+    # Adds %o as ordinal representation of the day
     def format_date(date, format)
       date = datetime(date)
       if format.nil? || format.empty? || format == "ordinal"
         date_formatted = ordinalize(date)
       else
+        format.gsub!(/%o/, '%%o')
         date_formatted = date.strftime(format)
+        date_formatted.gsub!(/%o/, ordinal(date.strftime('%e').to_i))
       end
       date_formatted
     end