Create iterator for batch operation

[UmanShahzad]

Create an iterator-based batch function, so that the user can loop over the batch call and get results per IP 1-by-1 rather than all at once, which is probably necessary for really large inputs whose outputs could exceed the available RAM on small machines e.g. in the cloud.

This is particularly useful after #37 because the user can input millions of IPs at once to the function.