Missing RR implementation & advanced usage

* Added support for MX, TXT, PTR, SOA, ANY, NS, AAAA records
* Added additional & authority message parsers & dumper (includes RobinvdVleuten's https://github.com/reactphp/react/pull/272)
* Fixed TCP retry parser & dumper. In TCP first two octets describe the length of data
* Added explain method to Message, Query, Record for detailed information in a dig like format.
* Added examples
* Message->questions now stores array of Query objects instead of array of array
Are you okay with keeping time tracking (meta) properties inside Message object?

How about moving it in Executor::prepareRequest() @ https://github.com/reactphp/dns/pull/8/files#diff-f0c69078c23517fdbdb160298dc1c791R43

Or including this inside Message::prepare()?