rss: add per-tag Atom feed at /rss/tags/:tag/updates.xml

- rss#tag_updates action: filters Page.heads by tag name, default
  locale, 20 items, same caching as updates feed
- tag_updates.xml.builder: Atom feed with CGI.escapeHTML on title
  and summary, consistent with updates.xml.builder
- tags/show.html.erb: add subscription link above article list
- routes: two routes per existing pattern (format-less + .:format
  constrained to /xml/)

1 files changed, 3 insertions, 0 deletions

diff --git a/config/routes.rb b/config/routes.rb
index 2df9d46..92f2452 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -70,6 +70,9 @@ Cccms::Application.routes.draw do
     get  'rss/updates.:format', :to => 'rss#updates', :as => :rss_feed,
            :constraints => { :format => /xml|rdf/ }
     get  'rss/recent_changes',  :to => 'rss#recent_changes'
+    get  'rss/tags/:tag/updates',         :to => 'rss#tag_updates', :as => :rss_tag
+    get  'rss/tags/:tag/updates.:format', :to => 'rss#tag_updates', :as => :rss_tag_feed,
+           :constraints => { :format => /xml/ }
 
     match 'galleries/*page_path' => 'content#render_gallery', :via => :get
     match '/*page_path'          => 'content#render_page', :as => :content, :via => :get