package.xml: Prepare for Ubuntu 20.04 / Python3

Fix LLT with current Eigen master branch

Return type of LLT::rankUpdate was changed from LLT (value) to LLT& (reference)

Sync submodule cmake

Improve packaging testing

Update cmake to include new _LIBRARIES fix

Return by ref when possible

Fix destruction of objects 

Sync submodule CMake

Sync submodule CMake

Fix packaging

Remove silly warnings