Function metfor::dew_point_from_p_and_mw

pub fn dew_point_from_p_and_mw<P>(pressure: P, mw: f64) -> Option<Celsius> where
    P: Pressure,
    HectoPascal: From<P>, 

Given a mixing ratio and pressure, calculate the dew point temperature. If saturation is assumed this is also the temperature.

Returns: The dew point.