[WIP] : add contour line and filled in surf mesh for vertex data

Hi,

I post a example to create contour line of surface mesh data. But I have some questions :
- Is there an interest for vispy project to do this ?
- What is it the best place to include this capability (like a visual object ?)
- Have you project about colormap because i need them ?

If there is an interest i work on it in september ...