Fix double hyphen markup.

Doc/lib/libhtmlparser.tex

@@ -109,9 +109,9 @@ base class implementation does nothing.
 \begin{methoddesc}{handle_comment}{data}
 This method is called when a comment is encountered.  The
 \var{comment} argument is a string containing the text between the
-\samp{<!-\-} and \samp{-\->} delimiters, but not the delimiters
-themselves.  For example, the comment \samp{<!--text-->} will cause
-this method to be called with the argument \code{'text'}.  It is
+\samp{{-}{-}} and \samp{{-}{-}} delimiters, but not the delimiters
+themselves.  For example, the comment \samp{<!{-}{-}text{-}{-}>} will
+cause this method to be called with the argument \code{'text'}.  It is
 intended to be overridden by a derived class; the base class
 implementation does nothing.
 \end{methoddesc}