static makeScaling(sx, sy) {
        return new Mat3([
            sx, 0, 0,
            0, sy, 0,
            0, 0, 1,
        ]);
    }
@function makeScaling
@memberof OpenSeadragon.Mat3
@static
@param {Number} sx The x value of the scaling
@param {Number} sy The y value of the scaling
@returns {OpenSeadragon.Mat3} A scaling matrix