title: Laravel QueryBuilder - hook before a query is executed
body: <p>I would like to alter queries before execution, like for example</p>
  
  <pre><code>Event::listen('which event?', function($query) {
      $query-&gt;where('foo', 'bar');
  });
  </code></pre>
  
  <p>so that a <code>Example::where('name', 'baz')-&gt;get()</code> would produce this sql code: </p>
  
  <p><code>select * from example where name = 'baz' and foo = 'bar'</code>.</p>
  
  <p>Is this possible?</p>