How does conversation history work?

Very fun project :)

I couldn't quite figure out from a quick first read of the code how to use conversation history. Like if I run this, it doesn't know what I just asked:

```python
r = lf.query('Who is Larry Page', lm=lm)
print(r)
# Larry Page is a prominent American computer scientist ...

r2 = lf.query('What did I just ask?', lm=lm)
print(r2)
# I'm sorry, but I can't recall or access previous interactions.
```