provide metrics

[etaty]

finagle expose lots of interesting metrics : https://twitter.github.io/finagle/guide/Metrics.html

requests A counter of the total number of successes + failures. success A counter of the total number of successes. request_latency_ms A histogram of the latency of requests in milliseconds. load A gauge of the current total number of outstanding requests. pending A gauge of the current total number of outstanding requests (same as “load”).

Also maybe expose the latency in the Future response, so maybe write a scala Future + metric container.