• Added: Support for If-Range, If-Match, If-None-Match, If-Modified-Since,
  If-Unmodified-Since.
• Changed: Brand new build system. Functionality is split up between Sabre,
  Sabre_HTTP, Sabre_DAV and Sabre_CalDAV packages. In addition to that a new
  non-pear package will be created with all this functionality combined.
• Changed: Autoloader moved to Sabre/autoload.php.
• Changed: The Allow: header is now more accurate, with appropriate HTTP methods
  per uri.
• Changed: Now throwing back Sabre_DAV_Exception_MethodNotAllowed on a few
  places where Sabre_DAV_Exception_NotImplemented was used.