Feature/779 state serialization

[davidhjp01]

closes #779

• Uses libcbor for (de)serialization.
• Overrides << and >> to (de)seserialize cosim::serialization::node object to std::o/istream
• Added state_serilization_test.cpp which is based on save_state_test.cpp for testing.
• Extended save_state_test.cpp for testing export and import of states to/from files
• Added print_ptree for replacing the previous << operator for pretty-printing cosim::serialization::node.
• Reads canGetAndSetFMUstate and canSerializeFMUstate cosim capabilities from modelDescrpition.xml and store them to cosim::model_description

TODOs

• Add missing comments to the new APIs.

[davidhjp01]

@kyllingstad, @restenb the PR is ready for your reviews :)

[davidhjp01]

I think we need to parse the following CoSimulation capabilities from each FMU's modelDescription file

• canGetAndSetFMUstate
• canSerializeFMUstate

so that users can check if they can export states from the FMUs they are running. I think FMUs not implementing these functions can throw exception or abruptly terminate?

[restenb]

I think we need to parse the following CoSimulation capabilities from each FMU's modelDescription file

• canGetAndSetFMUstate
• canSerializeFMUstate

so that users can check if they can export states from the FMUs they are running. I think FMUs not implementing these functions can throw exception or abruptly terminate?

Not sure what the behavior would be, but it makes sense to include this check in any case. An FMU that does not set these flags should not be possible to use with state saving.