reduce paragraph spacing in Doxygen's LaTeX output

doc/doxygen/refman.tex

@@ -16,6 +16,7 @@
 % See the GNU Lesser General Public License in COPYING.LGPL for more details.
 %
 \input{./version.sty}
+\setlength{\parskip}{0pt}
 \begin{titlepage}
 \vspace*{4cm}
 {\Huge \textbf{StarPU Handbook}}\\