code: function skewDEG(ax, ay) {
      return skew(ax * Math.PI / 180, ay * Math.PI / 180);
  }
docs: Calculate a skew matrix using DEG angles
  @param ax Skew on axis x
  @param ay Skew on axis y
  @returns {{a: number, b: number, c: number, e: number, d: number, f: number}} Affine matrix