added pendulum setup

[jenan007]

No description provided.

[zgbkdlm]

"""
TODOs:
1) float32 float64
2) Change the forward dynamics a bit
3) Try other resamplers that work
4) Run for 2000 iters and see what happens
5) Pre-train models. Two ways: autoencoder or regression.
"""

[zgbkdlm]

@jenan007 also pls move the file ./experiments/pendulum/diffusion.py to ./demos. This is the folder where you scratch for sanity test. When everything is finalised, create a new file in the experiments folder, and this file should not contain any plotting (except for your pendulum-generation part) but only saving for results (e.g., trained models and errors). Put plot files in ./experiments/summary.