Edit piecewise_polynomial_curve to piecewise_curve (make it more general using templates) / Add python binding for all types of piecewise curve / Edit std error thrown

Fix problem in cubic hermite curve extended to any interval (not only [0,1]) / Added all conversion between bezier, polynomial, cubic hermite / All test ok

Modification in bezier curve, now there is a T_min and T_max (Only T_max before). More logic for curve_conversion. Also modified split bezier curve : before bezier curve defined on [0,T] and we splitted it in ts => bc1 was defined on [0,ts] and bc2 on [0,T-ts]. Now, bezier curve defined on [T_min,T_max] is splitted in ts => bc1 defined on [T_min,ts] and bc2 defined on [ts,T_max].

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.

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

change namespace spline to curve in include folder, rename folder spline to curve, change in the CmakeList.txt