message: add withinDistance to isPointOnSlope
diff: *
  * @param p Point to check.
  * @param b Slope.
  + * @param withinDistance Optional distance of tolerance.
  * @returns true if point is on the slope
  */
  - export function isPointOnSlope(p: IPoint, slope: ISlope, withinDistance?: number): boolean {
  -
  + export function isPointOnSlope(p: IPoint, slope: ISlope, withinDistance = 0): boolean {
  if (slope.hasSlope) {
  // y = mx * b
  - return round(p[1] - (slope.slope * p[0] + slope.yIntercept)) === 0;
  + return Math.abs(p[1] - (slope.slope * p[0] + slope.yIntercept)) <= withinDistance;
  } else {
  //vertical slope
  - return round(p[0] - slope.line.origin[0]) === 0;
  + return Math.abs(p[0] - slope.line.origin[0]) <= withinDistance;
  }
  -
  }
  /**
  