title: How to count how many itens were created by day, week and month from DateTimeField()
body: <p>Having the following model:</p>
  <pre class="lang-py prettyprint-override"><code>class Objects(models.Model):
      created_at = models.DateTimeField(auto_now_add=True)
  </code></pre>
  <p>How can I count how many <code>Objects</code> were created by day, week and month, returning an integer number for each query?</p>