Support for GPT-3.5-Turbo

[ciaran-regan-ie]

Great project!

I am trying to get it to work with GPT-3.5-Turbo-Instruct which is using the same legacy endpoint as davinci-002. However GPT-3.5-Turbo-Instruct does not work as is, as it requires the following two parameters to be changed, due to changes in OpenAI's API:

max_tokens=1
 echo=true

More generally, it would be nice to have support for newer models, such as GPT-4. I'd be willing to help with the changes.