title: append query string to any form of URL
body: <p>I ask user to input a URL in a text-box and need to append a query string to it.</p>
  
  <p>Possible values of URLs can be like:</p>
  
  <ol>
  <li><p><a href="http://www.example.com">http://www.example.com</a></p></li>
  <li><p><a href="http://www.example.com/a/">http://www.example.com/a/</a></p></li>
  <li><p><a href="http://www.example.com/a/?q1=one">http://www.example.com/a/?q1=one</a></p></li>
  <li><p><a href="http://www.example.com/a.html">http://www.example.com/a.html</a></p></li>
  <li><p><a href="http://www.example.com/a.html?q1=one">http://www.example.com/a.html?q1=one</a></p></li>
  </ol>
  
  <p>Now I need to add query string to it like "q2=two", so that output would be like:</p>
  
  <ol>
  <li><p><a href="http://www.example.com/?q2=two">http://www.example.com/?q2=two</a></p></li>
  <li><p><a href="http://www.example.com/a/?q2=two">http://www.example.com/a/?q2=two</a></p></li>
  <li><p><a href="http://www.example.com/a/?q1=one&amp;q2=two">http://www.example.com/a/?q1=one&amp;q2=two</a></p></li>
  <li><p><a href="http://www.example.com/a.html?q2=two">http://www.example.com/a.html?q2=two</a></p></li>
  <li><p><a href="http://www.example.com/a.html?q1=one&amp;q2=two">http://www.example.com/a.html?q1=one&amp;q2=two</a></p></li>
  </ol>
  
  <p>How can I achieve the following using PHP?</p>