code: function (target) {
              var a = this.getBounds();
              var ax, ay;
  
              if (target instanceof me.Renderable) {
                  var b = target.getBounds();
                  ax = b.centerX - a.centerX;
                  ay = b.centerY - a.centerY;
              } else { // vector object
                  ax = target.x - a.centerX;
                  ay = target.y - a.centerY;
              }
  
              return Math.atan2(ay, ax);
          }
docs: return the angle to the specified target
  @name angleTo
  @memberOf me.Renderable
  @function
  @param {me.Renderable|me.Vector2d|me.Vector3d} target
  @return {Number} angle in radians