get() now checks how many recent requests there are for the domain of the
incoming URL. The hash of recent requests gets pruned of older requests.
If, after pruning, the maximum rate has not been reached, the time of the
request is stored in the hash (key=domain, value=time). Otherwise, the
URL is put aside for later processing. For now, this amounts to adding it
to a queue; code will later be added to manage this queue.