A simple DNS message and response implementation.
 It only supports name queries.

 good informations about dns:
     rfc1035
     http://technet.microsoft.com/en-us/library/dd197470(v=ws.10).aspx
     serveral more could be found via google.
 
 What we need:
 dns header 6 * 16bit
     16bit ID
     16bit Flags
       1bit request/response indicator (0 = request)
       4bit operation code / what operation to be done (0 = query)
       1bit authoritive answer / obviosly only used for responses
       1bit truncation / indicate that the message was to large for a UDP datagram
       1bit recursion desired / 1 to recurse the request (we normally want this)
       1bit recursion available / obvious
       3bit reserved / set to 000
       4bit return code / 0 means successfull, currently all other are wrong for us
     16bit Question count
     16bit Answer count
     16bit Authority count
     16bit Additional count
 
 1 question resource record (valriable len) our would look like this.
     question name: 0x09localhost0x00
     16bit question type: 0x0001 (for A record question)
     16bit question class: 0x0001 (represents the IN question class)

TYPE            value and meaning
========================================================
(removed all obsolete and experimental codes)
A               1 a host address
NS              2 an authoritative name server
CNAME           5 the canonical name for an alias
SOA             6 marks the start of a zone of authority
WKS             11 a well known service description
PTR             12 a domain name pointer
HINFO           13 host information
MINFO           14 mailbox or mail list information
MX              15 mail exchange
TXT             16 text strings

QTYPE values
========================================================
QTYPE fields appear in the question part of a query.  QTYPES are a
superset of TYPEs, hence all TYPEs are valid QTYPEs.  In addition, the
following QTYPEs are defined:

AXFR            252 A request for a transfer of an entire zone
*               255 A request for all records

CLASS values
========================================================
IN              1 the Internet
CH              3 the CHAOS class
HS              4 Hesiod [Dyer 87]


 Our hardcoded request message:
     434301000001000000000000096C6F63616C686F73740000010001
     ^   ^   ^               ^                     ^   ^
    ID   |   |               |                     |   |
     flags   |               |                     |   |
     one query               |                     |   |
        query name (localhost)                     |   |
                                                type   |
                                                   class

 OK, as i analyse the response i realize that my request was repeated back along
 with the answer. For now I assume this is the default behaviour of DNS.
 At least I can be sure that our DNS will always respond that way.
 
 The last 4 bytes of the answer record represent the ip address. We can savely
 assume this as currently we only query IPv4 A records. With these this should
 be always true.
 
 out complete response was:
     434381800001000100000000096c6f63616c686f73740000010001c00c000100010000000f00040a0100dc
            ^   ^   ^
     no error   |   |
      one request   |
         one response
 
 We cut of the headers and the request (as it was our own...we do not care about
 it), leaving us with:
     c00c000100010000000f00040a0100dc
     ^   ^   ^   ^       ^   ^
  nref   |   |   |       |   |
      type   |   |       |   |
         class   |       |   |
               TTL       |   |
         resource date len   |
            here starts our ip
 
 nref => is a reference of the name queried corresponding the
 DNS Packet Compression Schema:
     2bits: compression indicator (11 when compression is active)
     rest:  offset to name
 
 In our case this means the offset is 0x0c (12). The offset is the offset from
 the start of the message.