Adds Llama2 70B model experiment

langchain-experiments/compare-models.ipynb

...experiments/data/output/editors-llama-2-13b-chat-gptq.txt

...experiments/data/output/editors-llama-2-70b-chat-gptq.csv

...experiments/data/output/editors-llama-2-70b-chat-gptq.txt

...-experiments/data/output/editors-openai-gpt-3.5-turbo.csv

langchain-experiments/data/output/editors-openai-gpt-4.csv

langchain-experiments/lib/hf_llama2_13b_chat_gptq.py

langchain-experiments/lib/hf_llama2_70b_chat_gptq.py

langchain-experiments/readme.md