pub fn from_points(p: Point<f64>, q: Point<f64>) -> Line {
        let a = p.y - q.y;
        let b = q.x - p.x;
        let c = p.x * q.y - q.x * p.y;
        Line { a, b, c }
    }
Returns the `Line` that passes through p and q.
src/point.rs