optional format string

[rbucker]

The user provides a etcd key and the sidekick stores the IP address in that location, however, skyDNS uses a JSON formatted value that include a TTL. It would be helpful if the RUN command could include the format of the value in the go template format or at least Printf() format string.

[monder]

I initially thought about it, because some services require to expose port number for example, but decided to go with simpler approach. :)
I've pushed the v0.0.2 version which supports --format flag and changed the example to be compatible with SkyDNS.