Add ScalaCheck/property based testing into library

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One of the most common trends in this library is to check for specific properties in the code (e.g. does this major triad had a major third, followed by a minor third? Is the distance between them also reflect those intervals?). While the example based tests do provide a reasonable amount of reassurance, another nice quality to have would be extensive fuzzing testing through ScalaCheck or a similar property based testing library.

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A great introduction can be found here.