startTimer(labels, exemplarLabels) {
		return this.enableExemplars
			? startTimerWithExemplar.call(this, labels, exemplarLabels)()
			: startTimer.call(this, labels)();
	}
Start a timer that could be used to logging durations
@param {object} labels - Object with labels where key is the label key and value is label value. Can only be one level deep
@param {object} exemplarLabels - Object with labels for exemplar where key is the label key and value is label value. Can only be one level deep
@returns {function} - Function to invoke when you want to stop the timer and observe the duration in seconds
@example
var end = histogram.startTimer();
makeExpensiveXHRRequest(function(err, res) {
	const duration = end(); //Observe the duration of expensiveXHRRequest and returns duration in seconds
	console.log('Duration', duration);
});