add link to xpressive

[SVN r31206]

libs/libraries.htm

@@ -250,6 +250,8 @@ how to download, build, and install the libraries.</p>
     container, from Eric Friedman and Itay Maman.</li>
     <li><a href="wave/index.html">wave</a> -  Standards conformant
   implementation of the mandated C99/C++ preprocessor functionality packed behind an easy to use iterator interface, from Hartmut&nbsp;Kaiser </li>
+    <li><a href="xpressive/index.html">xpressive</a> - Regular expressions that can be written as strings or as expression templates,
+        and which can refer to each other and themselves recursively with the power of context-free grammars, from Eric Niebler.</li>
 </ul>
 
 <hr>
@@ -274,6 +276,8 @@ how to download, build, and install the libraries.</p>
     <li><a href="tokenizer/index.html">tokenizer</a> - Break of a string or other
       character sequence into a series of tokens, from John Bandela</li>
     <li><a href="wave/index.html">wave</a> - Standards conformant implementation of the mandated C99/C++ preprocessor functionality packed behind an easy to use iterator interface, from Hartmut&nbsp;Kaiser.</li>
+    <li><a href="xpressive/index.html">xpressive</a> - Regular expressions that can be written as strings or as expression templates,
+        and which can refer to each other and themselves recursively with the power of context-free grammars, from Eric Niebler.</li>
 </ul>
 
 <h3><a name="Containers">Containers</a></h3>