Function tuning_curve 

pub fn tuning_curve(
    binary_train: &[i32],
    stimulus_values: &[f64],
    n_bins: usize,
    dt: f64,
) -> (Vec<f64>, Vec<f64>)

Tuning curve: mean firing rate vs stimulus value. Dayan & Abbott 2001.

Returns (mean_rates, bin_centres).