title: return query based on date
body: <p>I have a data like this in mongodb</p>
  
  <pre><code>{ 
      "latitude" : "", 
      "longitude" : "", 
      "course" : "", 
      "battery" : "0", 
      "imei" : "0", 
      "altitude" : "F:3.82V", 
      "mcc" : "07", 
      "mnc" : "007B", 
      "lac" : "2A83", 
      "_id" : ObjectId("4f0eb2c406ab6a9d4d000003"), 
      "createdAt" : ISODate("2012-01-12T20:15:31Z") 
  }
  </code></pre>
  
  <p>How do I query <code>db.gpsdatas.find({'createdAt': ??what here??})</code>, so that it returns the above data result to me from the db?</p>