Add colors to terminal output

[g-linville]

Right now, everything just prints in the default color. I think it would be nice to have function calls show up in one color, output from the LLM show up in another etc., as this would make it easier to visually scan through the output of a single gptscript invocation.

[ibuildthecloud]

I agree :)

[cjellick]

TUI makes this better - it has colors :-)