Contour Plots

All most all of the forge objects have the option to let user provide per vertex attributes such as colors and alphas for rendering.

In the case of contour plots, I am not sure if per vertex colours or alphas makes any sense. One possible usage that i can see is per iosline color and alpha values.

@arrayfire/core-devel Any possible use cases of allowing per vertex colours/alphas ? An alternative to these per vertex attributes i thought off is using colormaps with isolines, which is the most common way of coloring contour lines from what i have seen so far.