Add etcd PolledConfigurationSource

[nightwolfzor]

etcd is a highly-available key value store for shared configuration and service discovery inspired by Zookeeper. We are using it with our Docker/CoreOS inspired stack. More here; https://github.com/coreos/etcd

etcd is being used in a number of other projects relating to service discover as well and we'd like to see in included in archaius!

Is there any interest? Has anyone started thinking about creating another service?

If not, something I'm thinking about doing so would anyone be open to include it in archaius? There would be a requirement to bring in etcd4j; https://github.com/jurmous/etcd4j

[howardyuan]

@nightwolfzor That seems an interesting idea. As long as we keep the dependencies in a separate module, I don't see any particular problems of introducing another data source here. People can chose which modules to include in there projects. Please feel free to submit a PR for this.

[chandrapersonal]

Is there any progress in this. I am doing proof of concept in this.

[spoon16]

#318

[spoon16]

@nightwolfzor can this be closed?