Modif for spline deriv constraint to exact cubic : delete spline_deriv_constraint.h and modifications in other classes and tests

Edit polynom to polynomial in all files. File polynom.h edited to polynomial.h and bezier_polynom_conversion.h to bezier_polynomial_conversion.h

Modified constructor (set time directly in constructor) / add getters for control points and their time corresponding

more efficient and stable binomial coefficients computation

See merge request jchemin/curves!1

Topic/doc spline

See merge request loco-3d/curves!5

Edit doc of cubic_spline, exact_cubic, quintic_spline, spline_deriv_constraint. Modify name of variables min and max to t_min and t_max.

CMake: clean

See merge request loco-3d/curves!3

Fix evaluation of bezier of degree 0 added, Edit doc on bezier_curve, Edit assert_allclose to assertTrue in test.py