Add support for VCM computation.
Merge branch 'FixLocalSurfelEstimator' of github.com:JacquesOlivierLachaud/DGtal into VCM

Need to merge while waiting for merge in master.
Fix bug in ElementaryConvolutionNormalVectorEstimator.h
Add hat functions.
Fix in ImplicitDigitalSurface.
Remove container vector<Point> from VCM.
First version of VCM on digital surfaces.
Small update.
VCM as a normal estimator.
Add operator-> to ConstAlias.
Fix CountedConstPtrOrConstPtr assignment.
Add True estimators for shapes and wrap a VCM surface normal estimator.
Add embed method in TrueDigitalSurfaceLocalEstimator.
Add gridstep in true estimator.
Add variable kernel function for VCM.
Add access to eigenvalues in VCMOnSurface.
Fix error in pragma in VoronoiCovarianceMeasureOnDigitalSurface.h
Add operator== and operator!= in CountedxxxPtrOrxxxPtr. Improve doc.
Add initialization of eigenvalues.
Merge branch 'VCM' of github.com:JacquesOlivierLachaud/DGtal into VCM

Solve conflict