Add doc-strings for List exception members

src/include/List.h

@@ -12,7 +12,12 @@
  */
 class ListOutOfBoundsException: public std::exception {
 protected:
-	int min_index, max_index, requested_index;
+	//! \brief Minimum index defined in the list.
+	int min_index;
+	//! \brief Maximum index defined in the list.
+	int max_index;
+	//! \brief Index requested by user.
+	int requested_index;
 
 public:
 	/**