Function robust::incircle

pub fn incircle<T: Into<f64>>(
    pa: Coord<T>, 
    pb: Coord<T>, 
    pc: Coord<T>, 
    pd: Coord<T>
) -> f64

Returns a positive value if the coordinate pd lies outside the circle passing through pa, pb, and pc.
Returns a negative value if it lies inside the circle.
Returns 0 if the four points are cocircular.