Time shifting

Time Shifting

In "default mode" tracepusher starts a trace now and finishes it SPAN_TIME_IN_SECONDS in the future.

You may want to push timings for traces that have already occurred (eg. shell scripts). See https://github.com/agardnerIT/tracepusher/issues/4.

--time-shift true means start and end times will be shifted back by whatever is specified as the --duration.