title: HttpUtility.UrlEncode with uppercase hex characters
body: <p><code>HttpUtility.UrlEncode("abc : 123")</code> produces <code>abc+%3a+123</code> but I need it to produce <code>abc+%3A+123</code> (notice the uppercase <code>A</code>.</p>
  
  <p>Is there a way to have UrlEncode output uppercase hex characters?</p>
  
  <p>I don't want to simply call <code>.ToUpper()</code> on the entire string because I need <code>abc</code> to stay lowercase.</p>