[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)
[ISSUE-95] Added copyright notice to udp.go, udp_linux.go & udp_other.go
Merge branch 'ISSUE-95' of https://github.com/EverythingMe/dns into udp
Cleanup the pull request somewhat
It compiles
Cleanup the PR a bit

Remove code and simplify some functions. Documentation is still on the
todo.
Also don't export any of these functions and/or types.
even shorter
Fix the function documentation