add a round-robin scoring function

[NoamGaash]

Goal

when the user makes several requests to the same resource, replay those request in the same order as it was recorded. for example: GET api/count returns {"count": 1} GET api/count returns {"count": 2} GET api/count returns {"count": 3}

when recording and when replaying, we want to achieve the same behaviour.

usage:

    await advancedRouteFromHAR(/api/, {
        matcher: baseMatcher({
            scoring: roundRobin
        })
    });

[yuriteixeira]

This is the missing piece for my project. Would be awesome to have this feature (and thanks for this lib, btw... it saved us).