pub fn keltner(
high: &[f64],
low: &[f64],
close: &[f64],
params: KeltnerParams,
) -> FinanceResult<KeltnerSeries>pub fn keltner(
high: &[f64],
low: &[f64],
close: &[f64],
params: KeltnerParams,
) -> FinanceResult<KeltnerSeries>