Removed superfluous 'tracks' directory at the root of the repository.

Testing commits to github.

app/models/tag.rb

@@ -0,0 +1,11 @@
+class Tag < ActiveRecord::Base
+  has_many_polymorphs :taggables,
+                      :from => [:todos], 
+                      :through => :taggings,
+                      :dependent => :destroy
+
+  def on(taggable, user)
+    tagging = taggings.create :taggable => taggable, :user => user
+  end
+
+end