* core: allow all CIDR ranges in zone specifications
Allow (e.g.) a v4 reverse on a /17. If a zone is specified in such a
way a FilterFunc is set in the config. This filter is checked against
incoming queries.
For all other queries this adds a 'x != nil' check which will not impact
performace too much. Benchmark function is added as well to check for
this as wel.
Add multiple tests in tests/server_reverse_test.go.
Benchmark shows in the non-reverse case this hardly impact the speed:
~~~
classless:
pkg: github.com/coredns/coredns/core/dnsserver
BenchmarkCoreServeDNS-4 1000000 1431 ns/op 16 B/op 1 allocs/op
pkg: github.com/coredns/coredns/core/dnsserver
BenchmarkCoreServeDNS-4 1000000 1429 ns/op 16 B/op 1 allocs/op
master:
pkg: github.com/coredns/coredns/core/dnsserver
BenchmarkCoreServeDNS-4 1000000 1412 ns/op 16 B/op 1 allocs/op
pkg: github.com/coredns/coredns/core/dnsserver
BenchmarkCoreServeDNS-4 1000000 1429 ns/op 16 B/op 1 allocs/op
~~~
* README.md updates
