Scale = function(degrees, tuning) {
    this.degrees = degrees;
    this.tuning = tuning || new EqualTemperamentTuning(12);
}
Representation of a generic musical scale.  Can be subclassed to produce
specific scales.

@constructor
@param {Number[]} degrees Array of integer degrees.
@param {Tuning} [tuning] The scale's tuning.  Defaults to 12-tone ET.