Add DNS example (needs mirage-types 1.1.1 to work)
correct listening_port in dns
Add the skeleton for a DNS resolver as well.

This will move into mirage-dns shortly, but it's helpful to write
out the code here first.
fix to dns.0.8.0 api
Merge pull request #31 from avsm/master

Add DNS example (needs mirage-types 1.1.1 to work)