spf.go
func New(domain string, dnsResolver dns.DnsResolver) (*SPF, error) {
	return newSPF(domain, dnsResolver, 0, 0)
}
func New(domain string, dnsResolver dns.DnsResolver) (*SPF, error) {
	return newSPF(domain, dnsResolver, 0, 0)
}
// New create a new SPF instance
// fully loaded with all the SPF directives
// (so no more DNS lookups must be done after constructing the instance)