Support for multiple editor instances (Multiplayer Playmode)

[RyanGarber]

Unity now has an official multiplayer mode, which launches multiple editor instances. This feature is trivially easy to support -- the only issue when using it is that Acoustics attempts to delete the "old" cached ace file, but it's in use. Specifically, this line:

void InitAcoustics()
{
    ...
    var dataPath = System.IO.Path.Combine(Application.temporaryCachePath, AceFile.name);
    ...
}

By simply adding a suffix to the file, there's no more conflict. You could even simply expose an option for the user -- SetCachePath() or SetCacheId().