Change namespace and edit names in spline to curve for more generalization

CMakeLists.txt

cmake

include/curve/CMakeLists.txt

include/curve/MathDefs.h

include/curve/bernstein.h

include/curve/bezier_curve.h

include/curve/bezier_polynom_conversion.h

include/curve/cubic_spline.h

include/curve/curve_abc.h

include/curve/curve_constraint.h

include/curve/exact_cubic.h

include/curve/helpers/CMakeLists.txt

include/curve/helpers/effector_spline.h

include/curve/helpers/effector_spline_rotation.h

include/curve/linear_variable.h

include/curve/polynom.h

include/curve/quintic_spline.h

include/curve/spline_deriv_constraint.h

python/CMakeLists.txt

python/curve_python.cpp