(#464) Add netmap feature

(#464) Add the ability to manage netmap rules.

Change resource_map in iptables provider to map "--to" parameter, which allows for parsing of existing netmap rules in rules_to_hash method.

Change resource_list in iptables provider to map append "--to" parameter when inserting netmap rules.

Add firewall type property "to".

Add feature netmap.

Example:
firewall { "151 NAT rules":
  ensure     => "present",
  chain      => "PREROUTING",
  jump       => "NETMAP",
  destination => "10.168.34.0/24",
  to => "192.168.34.0/24",
  table => "nat",
  source => "192.168.1.0/24",
  proto => "all",
}