Support for function calling

[vwchu]

Hi, I am wondering if you could add Function calling support that was added in gpt-3.5-turbo-0613. I've been able to use raw mode to implement my own using this package but it would be nice to have it like token mode, but for the arguments field in function_call.

https://platform.openai.com/docs/guides/gpt/function-calling

[mosnicholas]

@ctjlewis curious if this is on the roadmap? :)