serialization via cereal working and tested

[vincentberenz]

What is new

• The shared memory has now a serialize and a deserialize methods, which allows to store arbitrary instances into the shared memory. Cereal is used in the background.

• There is a Serializer object which allows to serialize / deserialize object (without writing them in the shared memory) to encapsulate calls to Cereal.

• the exchange_manager_consumer and exchange_manager_producer have been updated to use this serialization (was previously casting instances to array of doubles)

Tests

Unit tests added

Demos

serialization.cpp added

Benchmark

serialization_frequency.cpp added. Not really a benchmark, just check how fast serialization is.

[MaximilienNaveau]

I think it is good, for each demos we should add a proper documentation in doxygen. (To be done in a next pull request)