Change soundFinished event parameters

@AmbientOSX In conjunction with virtual-world-framework/mars-game#190
The format here was to keep the object returned consistent with other usage of what we're calling an "instanceHandle" (consisting of a soundName and ID). It is encapsulated in an array here to potentially allow for other parameters outside of that object to be passed... at least that's how I understand it. Was there a problem accessing this or was it simply not working in the prior format?