[doc] slightly restructure the modules to group various utitlities

doc/doxygen/modules.txt

@@ -8,9 +8,32 @@
   @ingroup Common
 */
 
+/**
+  @defgroup Utilities Utilities
+  @brief Collection of helper classes, type traits, etc.
+  @ingroup Common
+*/
+
+/**
+  @defgroup Path Filesystem Paths
+  @brief Utilities for filesystem path management
+  @ingroup Utilities
+*/
+
+/**
+  @defgroup StringUtilities String Utilities
+  @brief Utility functions for std::string
+  @ingroup Utilities
+*/
+
+/**
+  @defgroup TupleUtilities Tuple Utilities
+  @brief Utility classes which can be used with std::tuple
+  @ingroup Utilities
+*/
 
 /**
   @defgroup TypeUtilities Type Utilities
   @brief Type traits, overload helpers, and other utilities for type computations
-  @ingroup Common
+  @ingroup Utilities
 */

dune/common/path.hh

@@ -7,8 +7,7 @@
 
 namespace Dune {
   /**
-   * @addtogroup Path Filesystem Paths
-   * @ingroup Common
+   * @addtogroup Path
    * @{
    */
 

dune/common/stringutility.hh

@@ -22,11 +22,11 @@
 
 namespace Dune {
 
-   /** @addtogroup Common
-
-          @{
-   */
-
+   /**
+    * @addtogroup StringUtilities
+    *
+    * @{
+    */
 
   /** \brief Check whether a character container has a given prefix
    *

dune/common/tupleutility.hh

@@ -14,7 +14,7 @@
 
 namespace Dune {
 
-  /** @ addtogroup Common
+  /** @addtogroup TupleUtilities
    *
    * @{
    */