- add link to the datetime module

Doc/lib/libtime.tex

@@ -426,6 +426,7 @@ usually located at \file{/usr/share/zoneinfo}. For example,
 
 
 \begin{seealso}
+  \seemodule{datetime}{More object-oriented interface to dates and times.}
   \seemodule{locale}{Internationalization services.  The locale
                      settings can affect the return values for some of 
                      the functions in the \module{time} module.}