Add IsMsg()

A quick validating function that checks if a buffer is a valid
DNS message.
The code is *far* from complete.
added comment/todo
Add Copy test
Merge branch 'master' of github.com:miekg/dns
comment
Add Class parsing test function
Add more EDNS0 options
Small extension of documentation
Added godnsagent to the list of users
Merge pull request #93 from DSpeichert/master

Added godnsagent to the list of users
Added our discodns project to the list
Merge pull request #94 from tarnfeld/readme-projects-discodns

Added our discodns project to the list
[ISSUE-95] Send replies from the right source IP address

Fixes #95
[ISSUE-95] Fixed IPv6 handling, reduced OOB buffer size to 40 bytes
Added Omri Bahumi to the CONTRIBUTORS file
[ISSUE-95] Added some documentation for the new UDP implementation
[ISSUE-95] Patch only relevant stacks (v4, v6, dual)
Add v6 benchmarking test.

Mostly to exercise the v6 serving path (of which most lies in the
standard library). But it also is a good test of v6 functionality.
Added .travis.yml for Travis-CI
Added travis build status to README.md