Support for <deformable>

[ManifoldFR]

Recently, Bullet C++ and PyBullet have started supporting the <deformable> tag in URDF files following this commit, see this file for a use example. I'm not sure of how it would integrate with pyrender though.

I recently used this package to make a rigid-body URDF using a sliced-up version of hand mesh I have, and it would be nice to use it again to make a URDF with a soft body mesh.