vchoutas/smplx ? reverse-engineered prompt

Build me a small Python package for working with SMPL X style human body models, so I can load a model from a local folder, choose between SMPL X, SMPL plus H, SMPL, or MANO, and get back the mesh and joints for a given pose, shape, and facial expression.

I also want a simple example script that opens a neutral model, shows the 3D body in a viewer, and can optionally plot the joints. If it helps, include a couple of example scripts for checking vertex correspondences for the face and hand mappings too.

Please make it easy to install and run with the model files I already downloaded, and include clear notes on where those files should go. If you need current viewer or plotting docs, look them up online.