Add .perpendicular() function in Geometry module (adapted from Eigen1)

Documentation:
 * add an overview for each module.
 * add an example for .all() and Cwise::operator<

Eigen/src/QR/EigenSolver.h

@@ -25,7 +25,9 @@
 #ifndef EIGEN_EIGENSOLVER_H
 #define EIGEN_EIGENSOLVER_H
 
-/** \class EigenSolver
+/** \ingroup QR_Module
+  *
+  * \class EigenSolver
   *
   * \brief Eigen values/vectors solver for non selfadjoint matrices
   *

Eigen/src/QR/HessenbergDecomposition.h

@@ -25,7 +25,9 @@
 #ifndef EIGEN_HESSENBERGDECOMPOSITION_H
 #define EIGEN_HESSENBERGDECOMPOSITION_H
 
-/** \class HessenbergDecomposition
+/** \ingroup QR_Module
+  *
+  * \class HessenbergDecomposition
   *
   * \brief Reduces a squared matrix to an Hessemberg form
   *

Eigen/src/QR/QR.h

@@ -25,7 +25,9 @@
 #ifndef EIGEN_QR_H
 #define EIGEN_QR_H
 
-/** \class QR
+/** \ingroup QR_Module
+  *
+  * \class QR
   *
   * \brief QR decomposition of a matrix
   *

Eigen/src/QR/SelfAdjointEigenSolver.h

@@ -25,7 +25,7 @@
 #ifndef EIGEN_SELFADJOINTEIGENSOLVER_H
 #define EIGEN_SELFADJOINTEIGENSOLVER_H
 
-/** \qr_module
+/** \qr_module \ingroup QR_Module
   *
   * \class SelfAdjointEigenSolver
   *

Eigen/src/QR/Tridiagonalization.h

@@ -25,7 +25,9 @@
 #ifndef EIGEN_TRIDIAGONALIZATION_H
 #define EIGEN_TRIDIAGONALIZATION_H
 
-/** \class Tridiagonalization
+/** \ingroup QR_Module
+  *
+  * \class Tridiagonalization
   *
   * \brief Trigiagonal decomposition of a selfadjoint matrix
   *