title: Select2 multiple-select - programmatically deselect/unselect item
body: <p>I have a select2 list and a set of external buttons. I wanted to click the external buttons and unselect corresponding items in the select2 list. I know I can do item selection from external value using the command </p>
  
  <pre><code>$("#external_btn").click(function() {
      $("#select2").val("CA").trigger("change");
  });  
  </code></pre>
  
  <p>So when I click on the "external_btn" button, the "ca" item will be selected on the select2.</p>
  
  <p>But how I can do item unselection? Thanks.</p>