Pensky-Alek-ReShapeUp

the default constructor (no parameters) should always set fields to default values.  A class always has a default constructor, but if we add a constructor with parameters, the default constructor no longer exists.  While this program doesn't call the default constructor for Line - we should always provide one, like:
```
public Line() {
    start = new Point();
    end = new Point();
}

public Line(Point s, Point e) {
    start = s;
    end = e;
}
```