[feature request] Add support for templates.

[codetalker7]

Apologies in advanced if I'm wrong, but I don't think there's any support for prompt templates (I didn't find anything in the README, atleast)? If not, it'll be really nice to have this. For instance, something even as simple as system/user prompt templates (instead of whole chat templates) will be great.

As a usecase, I want to set the system prompt to something like:

system_message = "You are an expert in the {language} programming language. Your job is to assist the user in writing nice programs in {language}".

where {language} can be filled in.