Llama2 13B chat config and code improvements

[agrogov]

• Added Dev Container for quick start in fresh env
• Added Llama2 13B chat config
• Moved merge to separate script due to memory issues after training
• Made some code improvements

[georgesung]

Thanks a lot for your PR! There were some helpful changes to the code organization for sure. However, since this repo is still a personal tinkering space for me, I don't want to hard-code the device map to 2 GPUs for example (e.g. I'm running on a single GPU for now, maybe a 4-GPU machine in the future, or 8-GPU, etc.). Also I haven't set up a Docker container to run this so I can't test the Dockerfiles, but it's a great idea!

You can make a fork of this repo for your use cases though. Again, thanks for the PR, there were some very good ideas here I may incorporate in the future.

[agrogov]

No problem! :)