Part of #103.

This would remove the last Boost dependency that requires linking. Also since Cereal is header-only we would work around the problem with _GLIBCXX_DEBUG ABI incompatibilities.

TODO:

• Check that we can use the cereal from the system package manager.
• Clean up the serialization code (maybe using if constexpr).
• Check whether we can use load_and_construct to avoid having to define default constructors.
• Investigate how to serialize containers nicely, so that actual numbers show up in the JSON and not just base64 encoded binary.