example: tui-rs integration

[flisky]

Thanks you for this wonderful crate!

I'm trying to use it in tui-rs, another wonderful crate. And I did some (mininal) changes:

• render the chart into string, without println!.
• explicit width and height, making terminal_size optional.
• some cleanups (clippy, smaller output)
• add an example how to use it with tui-rs.

I just hope it help, and it's totally fine if you close PR.