Add comments for end of namespace

include/hpp/curve/bezier_curve.h

include/hpp/curve/bezier_polynom_conversion.h

include/hpp/curve/cubic_spline.h

include/hpp/curve/curve_abc.h

include/hpp/curve/curve_constraint.h

include/hpp/curve/exact_cubic.h

include/hpp/curve/polynom.h

include/hpp/curve/quintic_spline.h

include/hpp/curve/spline_deriv_constraint.h

python/spline_python.cpp