Added iterator plugin for listing categories freely.

_plugins/iterator.rb

@@ -0,0 +1,43 @@
+module Jekyll
+  class Site
+    alias_method :orig_site_payload, :site_payload
+
+    # Constuct an array of hashes that will allow the user, using Liquid, to
+    # iterate through the keys of _kv_hash_ and be able to iterate through the
+    # elements under each key.
+    #
+    # Example:
+    #   categories = { 'Ruby' => [<Post>, <Post>] }
+    #   make_iterable(categories, :index => 'name', :items => 'posts')
+    # Will allow the user to iterate through all categories and then iterate
+    # though each post in the current category like so:
+    #   {% for category in site.categories %}
+    #     h1. {{ category.name }}
+    #     <ul>
+    #       {% for post in category.posts %}
+    #         <li>{{ post.title }}</li>
+    #       {% endfor %}
+    #       </ul>
+    #   {% endfor %}
+    # 
+    # Returns [ {<index> => <kv_hash_key>, <items> => kv_hash[<kv_hash_key>]}, ... ]
+    def make_iterable(kv_hash, options)
+      options = {:index => 'name', :items => 'items'}.merge(options)
+      result = []
+      kv_hash.sort.each do |key, value|
+        result << { options[:index] => key, options[:items] => value }
+      end
+      result
+    end
+
+    def site_payload
+      payload = orig_site_payload
+      payload['site']['iterable'] = {
+        'categories'  => make_iterable(self.categories, :index => 'name', :items => 'posts'),
+        'tags'        => make_iterable(self.tags, :index => 'name', :items => 'posts')
+      }
+      payload
+    end
+
+  end
+end