Add tuning documentation, add <content> tags back to most salmons,

make status pagination headers generation more lax about next page
existing

app/services/unfavourite_service.rb

@@ -13,10 +13,13 @@ class UnfavouriteService < BaseService
   private
 
   def build_xml(favourite)
+    description = "#{favourite.account.acct} no longer favourites a status by #{favourite.status.account.acct}"
+
     Nokogiri::XML::Builder.new do |xml|
       entry(xml, true) do
         unique_id xml, Time.now.utc, favourite.id, 'Favourite'
-        title xml, "#{favourite.account.acct} no longer favourites a status by #{favourite.status.account.acct}"
+        title xml, description
+        content xml, description
 
         author(xml) do
           include_author xml, favourite.account