Math: hide macro from Doxygen.

For some weird reason it caused Doxygen to use that as target for
documentation block that is *after* the macro.

src/Magnum/Math/Matrix3.h

@@ -319,7 +319,9 @@ template<class T> class Matrix3: public Matrix3x3<T> {
         MAGNUM_MATRIX_SUBCLASS_IMPLEMENTATION(3, Matrix3, Vector3)
 };
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
 MAGNUM_MATRIXn_OPERATOR_IMPLEMENTATION(3, Matrix3)
+#endif
 
 /** @debugoperator{Magnum::Math::Matrix3} */
 template<class T> inline Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Matrix3<T>& value) {

src/Magnum/Math/Matrix4.h

@@ -391,7 +391,9 @@ template<class T> class Matrix4: public Matrix4x4<T> {
         MAGNUM_MATRIX_SUBCLASS_IMPLEMENTATION(4, Matrix4, Vector4)
 };
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
 MAGNUM_MATRIXn_OPERATOR_IMPLEMENTATION(4, Matrix4)
+#endif
 
 /** @debugoperator{Magnum::Math::Matrix4} */
 template<class T> inline Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Matrix4<T>& value) {

src/Magnum/Math/Vector2.h

@@ -160,7 +160,9 @@ template<class T> class Vector2: public Vector<2, T> {
         MAGNUM_VECTOR_SUBCLASS_IMPLEMENTATION(2, Vector2)
 };
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
 MAGNUM_VECTORn_OPERATOR_IMPLEMENTATION(2, Vector2)
+#endif
 
 /** @debugoperator{Magnum::Math::Vector2} */
 template<class T> inline Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Vector2<T>& value) {

src/Magnum/Math/Vector3.h

@@ -208,7 +208,9 @@ template<class T> class Vector3: public Vector<3, T> {
         MAGNUM_VECTOR_SUBCLASS_IMPLEMENTATION(3, Vector3)
 };
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
 MAGNUM_VECTORn_OPERATOR_IMPLEMENTATION(3, Vector3)
+#endif
 
 /** @debugoperator{Magnum::Math::Vector3} */
 template<class T> inline Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Vector3<T>& value) {

src/Magnum/Math/Vector4.h

@@ -172,7 +172,9 @@ template<class T> class Vector4: public Vector<4, T> {
         MAGNUM_VECTOR_SUBCLASS_IMPLEMENTATION(4, Vector4)
 };
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
 MAGNUM_VECTORn_OPERATOR_IMPLEMENTATION(4, Vector4)
+#endif
 
 /** @debugoperator{Magnum::Math::Vector4} */
 template<class T> inline Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Vector4<T>& value) {