Sketch-mode differentiable render

## 🚀 Feature
It would be nice to add Sketch Render support like in **OpenCV** with` find,draw contours`, be able to render object and having their sketch versions in a differentiable way. I think it can be done changing the render, since all the Pytorch3d Library is a modular and _Lior Wolf_ is already working on that from your group at FAIR.

[Paper - END TO END TRAINABLE ACTIVE CONTOURS VIA DIFFERENTIABLE RENDERING](https://arxiv.org/pdf/1912.00367.pdf)
[Code](https://github.com/shirgur/ACDRNet)

## Motivation
Sketch Retrieval's tasks are in high demand, be able to sketch a chair and retrieve it from a dataset like shapenet could empower potential line of research.

## Pitch
It can open another line of research on **sketch based 3d model retrieval.**