#58 MethodLogger: jcabi-loggable monitor thread shuts down upon interrupt

One significant change here is moving away from `ScheduledExecutorService` to a regular `ExecutorService` with a loop. The reason for this is that I couldn't find a way to interrupt the thread (or detect the interrupt status) for a thread created by a `ScheduledExecutorService`, which just seems to keep performing periodic executions until `cancel()` or `shutdown()` is invoked. Of course, suggestions for a more "elegant" implementation is welcome. :)