Function stdev 

pub fn stdev<YI, F>(y: YI) -> (F, usize)
where
    F: Float + Default + Sum,
    YI: Iterator + Clone,
    YI::Item: Borrow<F>,

Compute the standard deviation of the signal, y

Return the standard deviation and the number of points averaged

use approx::assert_relative_eq;
use sci_rs::stats::stdev;

let y: [f64; 5] = [1.,2.,3.,4.,5.];
assert_relative_eq!(1.41421356237, stdev(y.iter()).0, max_relative = 1e-8);

let y: &[f32] = &[];
assert_eq!((0f32, 0), stdev(y.iter()));