Provide a way to start/stop a timer in different parts without wrapping the code that runs

[marianoguerra]

there's an API on metrics to do this:

http://metrics.codahale.com/manual/core/#timers

but the metrics-clojure API only provides (as far as I can see on the docs) time! and time-fn!:

http://metrics-clojure.readthedocs.org/en/latest/metrics/timers.html#time

would it be possible to have an api to do something like:

(def timer (start-timer))

...

; somewhere else

(stop-timer timer)

(the example is just the first idea that came to my mind)