allow 'useMaximalCoordinates' and 'useFixedBase' in pybullet.loadURDF.
enable split impulse for btRigidBody, even in btMultiBodyDynamicsWorld.
allow initialization of velocity and apply force for btRigidBody in pybullet/shared memory API.
process contact parameters in URDF also for btRigidBody (friction, restitution etc)
add pybullet.setPhysicsEngineParameter with numSolverIterations, useSplitImpulse etc.