added to_arpa to ip4 addresses
updated readme
split ip6 and ip4 into separate files, added correct to_arpa for ip6
split ip6 and ip4 into separate files, added correct to_arpa for ip6
added gemfile, moved class back to 1 file
forgot to delete class files
Merge pull request #6 from wazoo/add-arpa-format

Add arpa format (wazoo)