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/alerts.rb

@@ -0,0 +1,49 @@
+require 'yaml'
+
+module Jekyll
+  
+  class AlertPage < Page
+    def initialize(site, base, lang, srcdir, src, dstdir, dst, date)
+      @site = site
+      @base = base
+      @dir = '/'+dstdir
+      @name = dst
+      self.process(dst)
+      self.read_yaml(File.join(base, srcdir), src)
+      self.data['lang'] = lang
+      self.data['date'] = date
+      self.data['layout'] = 'alert'
+      if dstdir == ''
+        self.data['redirect'] = src.split('.')[0]
+      else
+        self.data['category'] = 'alert'
+        if self.data.has_key?('alias')
+          site.pages << AlertPage.new(site, base, lang, srcdir, src, '', self.data['alias']+'.html', date)
+        end
+      end
+    end
+  end
+
+  class AlertPageGenerator < Generator
+    def generate(site)
+      #generate each alert based on templates
+      Dir.foreach('_alerts') do |file|
+        next if file == '.' or file == '..'
+        lang = 'en'
+        src = file
+        dst = file
+        srcdir = '_alerts'
+        dstdir = lang + '/alert'
+        date = dst.split('-')
+        next if date.length < 4
+        date = date[0] + '-' + date[1] + '-' + date[2]
+        next if !/^[0-9]{4}-[0-9]{2}-[0-9]{2}$/.match(date)
+        site.pages << AlertPage.new(site, site.source, lang, '_alerts', src, dstdir, dst, date)
+      end
+      #TODO alerts are only generated for english language,
+      #but they could also be translated at some point. They would however
+      #need to fallback to english when no translation is available.
+    end
+  end
+
+end