Add Scaling and Translation class as discussed on ML, still missing:

* handling Quaternion, AngleAxis and Rotation2D, 2 options here:
 1- make all of them inheriting a common base class Rotation such that we can
    have a single version of operator* for all the rotation type (they all get converted to a matrix)
 2- write a version for all type (so 3 rotations types * 3 for Transform,Translation and Scaling)
* real documentation

Eigen/Geometry

@@ -31,6 +31,8 @@ namespace Eigen {
 #include "src/Geometry/AngleAxis.h"
 #include "src/Geometry/Rotation.h"
 #include "src/Geometry/Transform.h"
+#include "src/Geometry/Translation.h"
+#include "src/Geometry/Scaling.h"
 #include "src/Geometry/Hyperplane.h"
 
 } // namespace Eigen