DevEx Improvements and Bug Squashing

[CyrusOfEden]

@henrycunh not sure why it's 8 commits but the diff is very small

[CyrusOfEden]

d187303 includes:

Bugs:

1. Appending empty CompletionMessages without the appropriate function_call context
2. Answer not containing function_result

Changes:

1. cursive.CursiveModel => cursive.CursiveLanguageModel

Improvements:

1. Functions and Pydantic BaseModels can now be passed directly as functions= or function_call= and
2. cursive.model.CursiveModel to support struct-generation a la jxnl instructor

[henrycunh]

Amazing, thanks for the contributions!

Do you want to write an example of the new improvements on the README?

[CyrusOfEden]

Updated the README!

[henrycunh]

Thanks @CyrusOfEden, amazing work!

[CyrusOfEden]

Ayyy awesome :)

Wen new release? :P