title: Get last created object for each user?
body: <p>I have a collection, say, "Things":</p>
  
  <pre><code>{ id: 1
      creator: 1
      created: Today }
  { id: 2
      creator: 2
      created: Today }
  { id: 3
      creator: 2
      created: Yesterday }
  </code></pre>
  
  <p>I'd like to create a query that'll return each Thing created by a set of users, but only their most recently created thing.</p>
  
  <p>What would this look like? I can get search my collection with an array of creators and it works just fine - how can I also only get the most recently created object per user?</p>
  
  <pre><code>Thing.find({ _creator : { "$in" : creatorArray })...
  </code></pre>