New contacts are bouncy, old are resting

If a contact is new (previous impluse = 0), then we treat it as bouncy (respecting restitution).
If the contact is old we treat it as resting.

Exceptions for restitutions <=0 and >= 1.

src/dynamics/solver/velocity_constraint.rs

@@ -239,13 +239,11 @@ impl VelocityConstraint {
                             + gcross1.gdot(gcross1)
                             + gcross2.gdot(gcross2));
 
-                    let mut rhs = (vel1 - vel2).dot(&force_dir1);
-
-                    if rhs <= -params.restitution_velocity_threshold {
-                        rhs += manifold_point.restitution * rhs
-                    }
-
-                    rhs += manifold_point.dist.max(0.0) * inv_dt;
+                    let rhs = if manifold_point.is_bouncy() {
+                        (1.0 + manifold_point.restitution) * (vel1 - vel2).dot(&force_dir1)
+                    } else {
+                        (vel1 - vel2).dot(&force_dir1) + manifold_point.dist.max(0.0) * inv_dt
+                    };
 
                     let impulse = manifold_point.data.impulse * warmstart_coeff;