• Moved the benchmarking code under benchmark/ so it won't be indexed
  by CPAN (Tim Brody).
  
• Avoid leaking memory inside extension elements by cleaning up on
  stylesheet DESTROY (Tim Brody).
  
• xsltInit() and xsltCleanupGlobals() to avoid leaking memory on
  init/shutdown (Tim Brody).
  
• Added support for stylesheet context functions via a
  $stylesheet->register_function() method with the same arguments as
  XML::LibXSLT->register_function(). (Tim Brody)
  
• Added support for register_element() on stylesheet objects. The callback
  may leak memory though - nothing frees the _private attributes of the
  node + document owner for the passed arguments? (Tim Brody)