Function pure_pursuit 

pub fn pure_pursuit(
    rx: f64,
    ry: f64,
    rtheta: f64,
    wx: f64,
    wy: f64,
    linear_v: f64,
) -> (f64, f64)

Pure Pursuit geometric path-tracking algorithm Returns (curvature_kappa, angular_velocity_w) given robot pose and target waypoint