Please add API key for LLM

[kidherofun]

@3yqq Here is a interesting found. Why not add a custom API key for user own?

[kidherofun]

@3yqq test

[malloc-realloc]

thank you, i will add this.

[malloc-realloc]

keyword llm added. (llm "your-llm") sets the llm variable in current environment. After setting llm, we call the llm stored in the llm variable. I think it's better to put api-key in the settings instead of in code.