- Enhance CMakeLists.txt files.
- Move to Boost Test from Google Test to support pre-C++11 compilers.
- Add more configurations on CI matrix builds.
- Other minor fixes
Previously the conversion would fail because struct object is not
generally provided for the const version of the type, but because
the wrapper would pass down the type unchanged, it would look for
exactly that missing template specialization unsuccessfully.
This is specifically an issue for std::reference_wrapper because
std::cref() returns an std::reference_wrapper<const T>.
