This works for IPv4 addresses but not IPv6

I only needed IPv4 for now but I will try to get back to this in the future.
Fix _commify sub
Make dump output valid JSON
Handle Math::Int128 objects in JSON output

Unfortunately there seems to be a bad interaction between JSON::XS and our
TO_JSON sub for Math::Int128 objects.
Add a test for the iterate_search_tree() method the dumper script needs