fix coloring of last `n_batch` of prompt, and refactor line input

[bitRAKE]

https://github.com/ggerganov/llama.cpp/blob/721311070e31464ac12bef9a4444093eb3eaebf7/main.cpp#L980-L983 This can fail to colorize the last params.n_batch part of the prompt correctly because embd was just loaded with those tokens and not printed, yet.

[sw]

Can confirm the bug and the PR fixes it and is certainly cleaner. Can you resolve the conflicts and maybe take along the one-liner in #283, also related to colors? Thanks.

[ggerganov]

@sw merge if you approve it