title: How do I tell my UITableViewCell to "auto-resize" when its content changes?
body: <p>In my cell.xib, I have a label, with constraints to all its sides. I've set that label to <code>lines = 0</code> and <code>line-break = word wrap</code>.  Then, I do this to my TableView:</p>
  
  <pre><code>self.tableView.rowHeight = UITableViewAutomaticDimension
  self.tableView.estimatedRowHeight = 100.0
  </code></pre>
  
  <p>Everything works great, and my UITableViewCell is auto-height.  If the text is long, then my tableView intelligently calculates the size.</p>
  
  <p>The problem is -- how do I tell my UITableView to "re-calculate" the size once the content changes in the cell?</p>
  
  <p>My cell could call its delegate, and in this delegate, I'd like the TableView to re-draw the height.</p>
  
  <p>Right now, the content in my cells change constantly, but the cell height never changes.</p>