Use IPv6 as canonical storage format (IPv4 -> IPv4-mapped IPv6).

Addresses GitHub issues #4 and maybe #5.
Merge remote-tracking branch 'origin/topic/jsiwek/fix-ipv6'

* origin/topic/jsiwek/fix-ipv6:
  Use IPv6 as canonical storage format (IPv4 -> IPv4-mapped IPv6).

BIT-1299 #merged