What Eric and Zakir said
Adding radix support to constraints

This allows us to lookup an index -> ip address much faster
(16 seconds for ~3.7 billion addresses with sparse blacklist,
vs 65 sec before radix array).

Setting the PREFIX_LEN to /20, as this appears to give a good tradeoff
between radix population time (<1ms), runtime (16s), and memory footprint (4MB).
add blacklist_lookup_index proto
constraints stores network order; we want to return host order
have cyclic use blacklist_lookup_index
Support multiple cyclic groups for smaller subnets

We will choose the first one in the list that is large enough to support
the number of hosts chosen. This speeds up scanning small networks considerably:
e.g. /16s can be scanned in <200ms (+ cooldown)
demote spurious log_infos to log_debug
Merge branch 'fast-whitelist' of github.com:zmap/zmap