Improved BeEF::Filters support for IPv4 and IPV6.

Changed regex in #is_valid_ip? to be more strict since it previously
would have matched an invalid IP such as 999.999.999.999. Changed its
name to #is_valid_ipv4?.

Added new #is_valid_ipv6? method that validates IPv6 addresses. It is
very comprehensive and will match normal IPv6 addresses, zero
compressed, link-local with zone index, and IPv6 addresses that have
IPv4 embedded, mapped, and translated.

Added new #is_valid_domain? method that validates domain names.
Updated #validate_response to use BeEF::Filters.