Implement polling functionality

[niltooth]

It would be very useful to be able to ping/poll a service globally and receive multiple responses (one from each copy of the service running).

It would also be helpful to be able to append some token to the end of the subject on both client & server side. This would allow for polling of different subsets of the same service e.g. by region,datacenter or environment.

[cdevienne]

@dev-mull could you give my PR a try? I think it covers your need.