Implement Cross-Origin Resource Sharing:

* Add Api::ApplicationController
* Route OPTION requests (CORS preflight) to API application controller
* Filter all API requests through #cor_filter in API application
  controller

app/controllers/api/application_controller.rb

@@ -0,0 +1,14 @@
+class Api::ApplicationController < ApplicationController
+  before_filter :cor_filter
+
+  def cor_filter
+    headers['Access-Control-Allow-Origin'] = request.headers['Origin']
+  end
+
+  def cor_preflight
+    headers['Access-Control-Allow-Methods'] = 'GET, POST, PUT, DELETE'
+    headers['Access-Control-Allow-Headers'] = 'Content-Type, X-Requested-With'
+
+    head :ok
+  end
+end

app/controllers/api/v0/playlists_controller.rb

@@ -1,4 +1,4 @@
-class Api::V0::PlaylistsController < ApplicationController
+class Api::V0::PlaylistsController < Api::ApplicationController
   respond_to :json
 
   def index