Split of service.go into msg/service.go

Create a new package called 'msg', just like for SkyDNS1. This
is need because some transformation function will be used
outside SkyDNS.

The methods names in there need to be cleaned up slightly.
Create Path and PathWithWildcard

Use Path to create an etcd path, the opposite operation is done
with Domain. Use PathWithWildcard when there are wildcards in
the name. This last funcion needs to be exported because SkyDNS
needs it.
Merge branch 'master' of github.com:skynetservices/skydns