Go bindings for iptables utility.

In-kernel netfilter does not have a good userspace API. The tables are
manipulated via setsockopt that sets/replaces the entire table. Changes to
existing table need to be resolved by userspace code which is difficult and
error-prone. Netfilter developers heavily advocate using iptables utlity for
programmatic manipulation.

go-iptables wraps invocation of iptables utility with functions to append and
delete rules; create, clear and delete chains.