Add link to the gmpy project.

Doc/lib/libmpz.tex

@@ -96,3 +96,11 @@ An mpz-number has one method:
   The mpz-number must have a value greater than or equal to zero,
   otherwise \exception{ValueError} will be raised.
 \end{methoddesc}
+
+
+\begin{seealso}
+  \seetitle[http://gmpy.sourceforge.net/]{General Multiprecision Python}{
+            This project is building new numeric types to allow
+            arbitrary-precision arithmetic in Python.  Their first
+            efforts are also based on the GNU MP library.}
+\end{seealso}