Refactoring

See merge request loco-3d/curves!1

Edit file name spline_python.cpp to curve_python.cpp, in test.py edit TestSpline and test_spline to TestCurve and test_curve, edit all makefiles, make test 100% OK

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

sync with hpp-spline master

fix python tests

And also check that AssertionErrors are not silenced

[BUG FIX] evalXXX methods do not consider time

tentative bug fix for extract

Use point_t::Zero(Dim) instead of point_t::Zero() 

Use point_t::Zero(Dim) instead of point_t::Zero()  because it is required to use a waypoint_t as templated type

DeCasteljau and Curve splitting 

Merge