title: update jquery select2 available choices for multiple instances
body: <p>I have two jquery select2 instances that have the same options and the same class
  I want that each time I select an option in one select2 instance it becomes not available in both instances</p>
  
  <pre><code>&lt;select class="select2-element" multiple="multiple"&gt; //instance 1
      &lt;option value="AL"&gt;Alabama&lt;/option&gt;
      ...
      &lt;option value="WY"&gt;Wyoming&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select class="select2-element" multiple="multiple"&gt; //instance 2
      &lt;option value="AL"&gt;Alabama&lt;/option&gt;
      ...
      &lt;option value="WY"&gt;Wyoming&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p><strong>EDIT</strong>
  For simplicity I mentioned that I have two select elements, but in reality I have x elements generated dynamically</p>