title: jsonpickle serialize object/list to a clean json string
body: <p>how to get an clean json string using  jsonpickle. 
  the output has lots of addtional fields that not in my class,for example,"py/reduce","_state","_django_version" and so on.</p>
  
  <p>i just want a clean output like this:</p>
  
  <pre><code>[
    {"name":"namevalue","id":"4","expiredtime":"2015-3-4 12:0000"},
    {"name":"namevalue2","id":"5","expiredtime":"2015-4-4 12:0000"}
  ]
  </code></pre>
  
  <p>i have tried add unpicklable=False ,but not work.</p>
  
  <pre><code> item_list=list(ChannelItem.objects.filter(channel__id=channel_id))
   results =[jsonpickle.encode(ob,unpicklable=False) for ob in item_list]
  </code></pre>
  
  <p>what i have missed? does jsonpickle can't serialize an object/objectlist to  an clean jsonstring that just contains the fields defined in the class? or is there an alternative package to do this? </p>