Version 0.3.8 of the "3D Function Surfaces" script. Applied patch by Elod Csirmaz

* Modified the "Add X,Y,Z Function Surface" part:
* Changed how wrapping is done to avoid generating unnecessary vertices and make the result more intuitive.
* Added helper functions the results of which can be used in x(u,v), y(u,v), z(u,v).
* The script can now close the ends of an U-wrapped surface.
* It's now possible to create multiple objects with one set of formulae.