Function num_biguint_from_u64_limbs 

pub fn num_biguint_from_u64_limbs<I>(limbs: I) -> BigUint
where
    I: IntoIterator,
    I::Item: Borrow<u64>,
    I::IntoIter: ExactSizeIterator,

Returns a BigUint from u64 limbs with little-endian ordering