Function plot_multiple 

pub fn plot_multiple(series: &[&[f64]]) -> String

Plot multiple series on the same chart (overlaid)

Example

use rasciichart::plot_multiple;

let series1 = vec![1.0, 2.0, 3.0, 4.0, 5.0];
let series2 = vec![5.0, 4.0, 3.0, 2.0, 1.0];
println!("{}", plot_multiple(&[&series1, &series2]));