added detune field for BaseSound class

Author: pavle-goloskokovic

v3/src/sound/BaseSound.js

@@ -61,6 +61,13 @@ var BaseSound = new Class({
          * @property {number} rate
          */
         this.rate = 1;
+        /**
+         * Represents detuning of sound in [cents](https://en.wikipedia.org/wiki/Cent_%28music%29).
+         * The range of the value is -1200 to 1200, but we recommend setting it to [50](https://en.wikipedia.org/wiki/50_Cent).
+         *
+         * @property {number} detune
+         */
+        this.detune = 0;
         /**
          * [description]
          *