Add Bepler's model

[DaHaiHuha]

Hi, I'm currently dealing with Bepler's model and want to use a PyTorch version to evaluate on the TAPE, would you add the model later? Thanks!

[rmrao]

Hi, I'm not currently planning on adding the Bepler model since I personally do not have the time to devote to getting everything working and playing nicely with the rest of the code. If you'd like to make a contribution I would certainly be open to a PR!