add the suffix Ref to doxygen link to reference

Modular_arithmetic/doc/Modular_arithmetic/CGAL/Modular_traits.h

@@ -2,7 +2,7 @@
 namespace CGAL {
 
 /*!
-\ingroup PkgModularArithmetic
+\ingroup PkgModularArithmeticRef
 
 An instance of `Modular_traits` is a model of `ModularTraits`, 
 where <span class="textsc">T</span> is the associated type. 

Modular_arithmetic/doc/Modular_arithmetic/CGAL/Residue.h

@@ -2,7 +2,7 @@
 namespace CGAL {
 
 /*!
-\ingroup PkgModularArithmetic
+\ingroup PkgModularArithmeticRef
 \anchor Residue 
 
 \brief The class `Residue` represents a finite field \f$ \mathbb{Z}{/p\mathbb{Z}}\f$, 

Modular_arithmetic/doc/Modular_arithmetic/PackageDescription.txt

@@ -1,14 +1,14 @@
-/// \defgroup PkgModularArithmetic Modular Arithmetic Reference
+/// \defgroup PkgModularArithmeticRef Modular Arithmetic Reference
 /// \defgroup PkgModularArithmeticConcepts Concepts
-/// \ingroup PkgModularArithmetic
+/// \ingroup PkgModularArithmeticRef
 /*!
-\addtogroup PkgModularArithmetic
+\addtogroup PkgModularArithmeticRef
 \cgalPkgDescriptionBegin{Modular Arithmetic,PkgModularArithmeticSummary}
 \cgalPkgPicture{Modular_arithmetic.png}
 \cgalPkgSummaryBegin
 \cgalPkgAuthors{Michael Hemmer and Sylvain Pion}
 \cgalPkgDesc{This package provides arithmetic over finite fields. The provided tools are in particular useful for filters based on  modular arithmetic and algorithms based on Chinese remainder. }
-\cgalPkgManuals{Chapter_Modular_Arithmetic,PkgModularArithmetic}
+\cgalPkgManuals{Chapter_Modular_Arithmetic,PkgModularArithmeticRef}
 \cgalPkgSummaryEnd
 \cgalPkgShortInfoBegin
 \cgalPkgSince{3.4}