First draft of btMultiBody serialization, including optional names for base, link and joints (see ImportURDFDemo/ImportURDFSetup.cpp how this is done)

Bump up version number to 2.84 because of new serialization data.

src/BulletDynamics/Featherstone/btMultiBodyLink.h

@@ -127,6 +127,9 @@ btVector3 m_appliedConstraintForce;    // In WORLD frame
 
 	btTransform	m_cachedWorldTransform;//this cache is updated when calling btMultiBody::forwardKinematics
 
+	const char* m_linkName;//m_linkName memory needs to be managed by the developer/user!
+	const char* m_jointName;//m_jointName memory needs to be managed by the developer/user!
+
     // ctor: set some sensible defaults
 	btMultibodyLink()
 		: 	m_mass(1),
@@ -138,8 +141,9 @@ btVector3 m_appliedConstraintForce;    // In WORLD frame
 			m_dofCount(0),
 			m_posVarCount(0),
 			m_jointType(btMultibodyLink::eInvalid),
-			m_jointFeedback(0)
-			
+			m_jointFeedback(0),
+			m_linkName(0),
+			m_jointName(0)
 	{
 		
 		m_inertiaLocal.setValue(1, 1, 1);