Volmdlr

Added
- handle spherical surfaces
- positionning of parts in STEP reading

Added
- step export

Changed
- modules -2D or *3D renamed in *2d, *3d
- point and vector declared with their x, y, z vm.Point2D((0, 0)) -> vm.Point2D(0, 0)
- separating in new modules: display, wires, edges...
- PEP8: method names
- PointAtCurvilinearAbscissa changed to point_at_abscissa
- MPLPlot changed to plot()
- plot now returns only ax instead of fig, ax

Added
- Calculate the distance between LineSegment3D/LS3D, Arc3D/LS3D, Arc3D/Arc3D and between CylindricalFace3D too.
- Use PlaneFace3D with contours2D in a classic way and use it with contours3D with a 'from_contours3d' as CylindricalFace3D does.
- Calculate the distance between CylindricalFace3D and PlaneFace3D.
- Calculate the distance between CylindricalFace3D, PlaneFace3D and ToroidalFace3D.
- contours2d.tessel_points which gives all points of a contour2d, and .points the end points of primitives.
- Implementation of ConicalFace3D in Core and RevolvedProfile.
- Implementation of SphericalFace3D in Core.
- BSplineFace3D works.

Changed
- cut_contours in Face3D which take all points from a Contour2D, not one side like before. Furthermore, it is light and quick.

- typings
- workflow to instanciate point

Added
- mesh module