made some progress in saving and restoring the state during the simulation, with identical results.

Option to de/serialize btPersistentContactManifolds and fix lossy conversion during btMultiBody de/serialization of base world transform
(serialize the quaternion, not the converted 3x3 matrix)
There are still several caches not taken into account, and btMultiBody links/constraints are not deserialized yet etc.
See examples\pybullet\examples\saveRestoreState.py for an example.

Extras/Serialize/BulletFileLoader/btBulletFile.h

@@ -59,6 +59,8 @@ namespace bParse {
 
 		btAlignedObjectArray<bStructHandle*>	m_dynamicsWorldInfo;
 
+		btAlignedObjectArray<bStructHandle*>	m_contactManifolds;
+
 		btAlignedObjectArray<char*>				m_dataBlocks;
 		btBulletFile();