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
My original thinking was to re-use `Message`'s constants. But now I am thinking that a better option would be to create a mapping-class which contains mapping between Human-Machine types/classes and use that instead of Reflecting `Message`.