[ML] PropertyVector: add docu.

MeshLib/PropertyVector.h

 /**
- * \file
- * \brief  Definition of the class Properties that implements a container of
- *         properties.
  *
  * \copyright
  * Copyright (c) 2012-2014, OpenGeoSys Community (http://www.opengeosys.org)
@@ -22,6 +19,10 @@
 namespace MeshLib
 {
 
+/// Class template PropertyVector is a std::vector with template parameter
+/// PROP_VAL_TYPE. The reason for the derivation of std::vector is
+/// the template specialisation for pointer types below.
+/// \tparam PROP_VAL_TYPE typical this is a scalar, a vector or a matrix
 template <typename PROP_VAL_TYPE>
 class PropertyVector : public std::vector<PROP_VAL_TYPE>
 {
@@ -35,16 +36,32 @@ public:
 	{}
 };
 
+/// Class template PropertyVector is a std::vector with template parameter
+/// T, where T is a pointer type.
+/// The behaviour has changed for the constructor, destructor and the operator[].
+/// The user has to provide the size and an item to group mapping for construction.
+/// The destructor takes care to delete the entries of the vector.
+/// The operator[] uses an item to group property map to access to the
+/// correct property.
+/// \tparam T pointer type, the type the type points to is typical a scalar,
+/// a vector or a matrix type
 template <typename T>
 class PropertyVector<T*> : public std::vector<T*>
 {
 public:
+	/// @param n_prop_groups number of different property values
+	/// @param item2group_mapping Class Mesh has a mapping from the mesh items
+	/// (Node or Element) to an index (position in the data structure).
+	/// The vector item2group_mapping must have the same number of entries as
+	/// the above mapping and the values have to be in the range
+	/// \f$[0, \text{n_prop_groups})\f$.
 	PropertyVector(std::size_t n_prop_groups,
 		std::vector<std::size_t> const& item2group_mapping)
 		: std::vector<T*>(n_prop_groups),
 		_item2group_mapping(item2group_mapping)
 	{}
 
+	/// Destructor ensures the deletion of the heap-constructed objects.
 	~PropertyVector()
 	{
 		std::for_each(
@@ -52,6 +69,8 @@ public:
 		);
 	}
 
+	/// The operator[] uses the item to group property map to access to the
+	/// correct property value/object.
 	T* const& operator[](std::size_t id) const
 	{
 		return (*static_cast<std::vector<T*> const*>(this))[_item2group_mapping[id]];