title: Laravel 4: validate checkbox at least one
body: <p>I need to validate checkbox array:</p>
  
  <pre><code>&lt;input name="cats[]" type="checkbox" value="1"&gt; sport
  &lt;input name="cats[]" type="checkbox" value="2"&gt; music
  &lt;input name="cats[]" type="checkbox" value="3"&gt; business
  </code></pre>
  
  <p>I found "array" validation in documentation:</p>
  
  <pre><code>Validator::make( 
      [ 'cats' =&gt; Input::get('cats') ],
      [ 'cats' =&gt; 'array' ]
  );
  </code></pre>
  
  <p>Is there any built-in way to check if at least one item checked? Also, how to check if values submitted match a given list?</p>