expose pybullet changeDynamics(spinningFriction=..., rollingFriction=..., restitution=...)

Bullet C-API b3ChangeDynamicsInfoSetSpinningFriction/RollingFriction/Resitution
b3PhysicsParamSetRestitutionVelocityThreshold, / pybullet.setPhysicsEngineParameter restitutionVelocityThreshold:
if the velocity is below this threshhold, the restitution is zero (this prevents energy buildup at near-resting state)
pybullet restitution.py example.

src/BulletDynamics/ConstraintSolver/btContactSolverInfo.h

@@ -62,6 +62,7 @@ struct btContactSolverInfoData
 	btScalar	m_maxGyroscopicForce;
 	btScalar	m_singleAxisRollingFrictionThreshold;
 	btScalar	m_leastSquaresResidualThreshold;
+	btScalar	m_restitutionVelocityThreshold;
 
 };
 
@@ -97,6 +98,7 @@ struct btContactSolverInfo : public btContactSolverInfoData
 		m_maxGyroscopicForce = 100.f; ///it is only used for 'explicit' version of gyroscopic force
 		m_singleAxisRollingFrictionThreshold = 1e30f;///if the velocity is above this threshold, it will use a single constraint row (axis), otherwise 3 rows.
 		m_leastSquaresResidualThreshold = 0.f;
+		m_restitutionVelocityThreshold = 0.2f;//if the relative velocity is below this threshold, there is zero restitution
 	}
 };