* Retrieve some code from what has been done on the ESP8266. Clarify a bit the signification of several bytes in the response.
* Add the type and class as members of the DNS class for an eventual future use.
* Clarify the sense of a magic number present in DNS server.
* A bit of aesthetics for the DNS server.
* Add a structure for the DNS question, use it DNS server to store the question data and to create the DNS answer from scratch.
