Fixed operator == in Point2, Point3, PointN. Right-hand operand no longer needs to be mutable.

Code in PointN uses v.data[i] instead of v[i] now

Point2 / Point3 use .x, .y, .z instead of data[0], data[1], data[2] in
operator <<

Made changes in Point2 / Point3 unit tests I missed earlier.