This is a companion to cidrsubnet that allows bulk-allocation of multiple
subnet addresses at once, with automatic numbering.
Unlike cidrsubnet, cidrsubnets allows each of the allocations to have a
different prefix length, and will pack the networks consecutively into the
given address space. cidrsubnets can potentially create more complicated
addressing schemes than cidrsubnet alone can, because it's able to take
into account the full set of requested prefix lengths rather than just
one at a time.