Function metfor::rh_ice

pub fn rh_ice<T1, T2>(temperature: T1, frost_point: T2) -> Option<f64> where
    T1: Temperature,
    T2: Temperature,
    Celsius: From<T1> + From<T2>, 

Calculate the relative humidity with respect to ice.

Returns: The relative humidity as a decimal, i.e. 0.95 instead of 95%.