title: tastypie : return reponse in xml format
body: <p>I read from the documentation that XML format is supported
  <a href="http://django-tastypie.readthedocs.org/en/latest/serialization.html#to-xml" rel="nofollow">http://django-tastypie.readthedocs.org/en/latest/serialization.html#to-xml</a>, however in current task, I only have to type <a href="http://url/api/entry/?format=json" rel="nofollow">http://url/api/entry/?format=json</a> in browser and define the correspond url in URL.py and the entry resource, the serialization of json is well taken care of. But for xml, there are extra things to do as I couldnt seem to find useful examples?</p>
  
  <pre><code>#urls.py
  entry_resource = EntryResource()
  urlpatterns = patterns('',
      url(r'^api/', include(entry_resource.urls)),
  )
  
  #entry class
  class EntryResource(Resource):
  ....
  ....fields
  
  class Meta:
      resource_name = 'entry'
      object_class = Entry
      ....
  </code></pre>