Add doxygen biref to ale.h (chaos-polymtl#1017)

Description of the problem
Doxygen missing in ale.h

Description of the solution
Add the required description.

How Has This Been Tested?
compile and inspect the doxygen output.

Future changes
parameters.h is next.

Comments
Since it is in the parameters namespace, the same description will be use in the parameters.h for declare and parse. I wanted to avoid the repetition of the description for declare and parse, but sometimes they differ a little bit, so I guess we should add the description everywher.

Former-commit-id: 23dbe56

Author: hepap

include/core/ale.h

@@ -23,39 +23,67 @@
 #include <deal.II/lac/vector.h>
 
 using namespace dealii;
-/**
- * The ALE class provides an interface for all common
- * element required for the introduction of the required terms for a moving
- *referential in the governing equations.
- **/
 
 namespace Parameters
 {
+  /**
+   * @brief An interface for all the common parameters required to consider
+   * a moving frame of reference in a simplified Arbitrary Lagrangian Eulerian
+   * (ALE) module.
+   *
+   * @tparam dim An integer that denotes the dimension of the space in which
+   * the problem is solved.
+   */
   template <int dim>
   class ALE
   {
   public:
+    /**
+     * @brief Construct a new ALE object.
+     */
     ALE()
     {
       velocity = std::make_shared<Functions::ParsedFunction<dim>>(dim);
     }
 
+
+    /**
+     * @brief Declare the parameters.
+     *
+     * @param[in,out] prm The ParameterHandler.
+     */
     virtual void
     declare_parameters(ParameterHandler &prm);
+
+    /**
+     * @brief Parse the parameters.
+     *
+     * @param[in,out] prm The ParameterHandler.
+     */
     virtual void
     parse_parameters(ParameterHandler &prm);
 
 
-    // ALE-Velocity function
+    /**
+     * @brief ALE velocity function
+     */
     std::shared_ptr<Functions::ParsedFunction<dim>> velocity;
 
+    /**
+     * @brief Return if the ALE module is enabled.
+     *
+     * @return enable A boolean that indicates if the ALE module is enabled.
+     */
     bool
     enabled() const
     {
       return enable;
     }
 
   private:
+    /**
+     * @brief Boolean indicating if the ALE module is enabled.
+     */
     bool enable;
   };