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
Still not a fan of this type of mutation on data objects. It's convenient to put it there, but it's not really part of the query data.