Function integrate 

pub fn integrate(
    f: &FnVec<'_>,
    a: f64,
    b: f64,
    epsabs: f64,
    epsrel: f64,
    key: i32,
    limit: usize,
    points: Vec<f64>,
    number_of_thread: usize,
    more_info: bool,
) -> Result<QagIntegrationResult, QagError>