[handbook] Use macro DumuxVersion for URLs

doc/handbook/3_tutorialimplicit.tex

@@ -248,7 +248,7 @@ of mixtures such as density or enthalpy are of interest. These
 interactions are defined by {\em fluid systems}, which are located in
 \verb+dumux/material/fluidsystems+. A more thorough overview of the
 \Dumux fluid framework can be found 
-at \url{http://www.dumux.org/doxygen-stable/html-2.11/modules.php}
+at \url{http://www.dumux.org/doxygen-stable/html-\DumuxVersion/modules.php}
 %in chapter~\ref{sec:fluidframework}.
 
 % In this example, a class for the definition of a two-phase system is used. This allows for the choice
@@ -412,7 +412,7 @@ To do that, you have to select different components via the property system in t
 If you want to take a closer look on how the fluid classes are defined and which
 substances are already available please browse through the files in the directory
 \texttt{/dumux/material/components} and read 
-the doxygen documentation \url{http://www.dumux.org/doxygen-stable/html-2.11/modules.php}.
+the doxygen documentation \url{http://www.dumux.org/doxygen-stable/html-\DumuxVersion/modules.php}.
 %chapter~\ref{sec:fluidframework}.
 
 \item \textbf{Use a Full-Fledged Fluid System} \\

doc/handbook/5_models.tex

@@ -127,7 +127,7 @@ $\boldsymbol{v}_\alpha$ & velocity (Darcy or free flow)& & \\
 \subsection{Available Models}
 We distinguish fully-implicit and sequential models. A list of all available models can be found
 in the Doxygen documentation at
-\url{http://www.dumux.org/doxygen-stable/html-2.11/modules.php}.
+\url{http://www.dumux.org/doxygen-stable/html-\DumuxVersion/modules.php}.
 The documentation includes a detailed description for every model.
 
 \subsubsection{Fully-Implicit Models}