Function merge_by_new

pub fn merge_by_new<I, J, F>(
    a: I,
    b: J,
    cmp: F,
) -> MergeBy<I::IntoIter, J::IntoIter, F> 
where
    I: IntoIterator,
    J: IntoIterator<Item = I::Item>,

Create a MergeBy iterator.