Add "Network status and alerts" page and RSS feed (fixes #170)

Generate alerts pages through alerts.rb plugin
Allow to keep short alias urls for each alert
Move alert pages in _alerts
Update sitemap plugin to include alerts

_plugins/catpage_for.rb

@@ -0,0 +1,49 @@
+#catpage_for allows to loop in site.pages sorted by custom page
+#variables and filtered by page.category.
+#Example : {% catpage_for p in site.pages sort_by:date category:release %}
+
+module Jekyll
+  module SortedForImpl
+    def render(context)
+      sorted_collection = collection_to_sort context
+      return if sorted_collection.empty?
+      sort_attr = @attributes['sort_by']
+      category_attr = @attributes['category']
+      #filter page by given category
+      s = []
+      for x in sorted_collection
+        if x.to_liquid.has_key?('category') && x.to_liquid['category'] == category_attr
+          s.push(x)
+        end
+      end
+      sorted_collection = s
+      #sort collection by given variable
+      sorted_collection = sorted_collection.sort_by { |i| i.to_liquid[sort_attr] }
+      #return modified array
+      original_name = @collection_name
+      result = nil
+      context.stack do
+        sorted_collection_name = "#{@collection_name}_sorted".sub('.', '_')
+        context[sorted_collection_name] = sorted_collection
+        @collection_name = sorted_collection_name
+        result = super
+        @collection_name = original_name
+      end
+      result
+    end
+  end
+ 
+  class SortedForTag < Liquid::For
+    include SortedForImpl
+ 
+    def collection_to_sort(context)
+      return context[@collection_name].dup
+    end
+ 
+    def end_tag
+      'endcatpage_for'
+    end
+  end
+end
+ 
+Liquid::Template.register_tag('catpage_for', Jekyll::SortedForTag)