title: Find substring range of NSString with unicode characters
body: <p>If I have a string like this.</p>
  
  <pre><code>NSString *string = @"1357"
  </code></pre>
  
  <p>To get a substring like <code>@"35"</code> you have to account for the fact the smiley face character take two bytes.</p>
  
  <pre><code>NSString *substring = [string substringWithRange:NSMakeRange(5, 4)];
  </code></pre>
  
  <p>Is there a way to get the same substring by using the actual character index so <code>NSMakeRange(3, 3)</code> in this case?</p>