Since CMake 3.19 it is possible to specify private sources for `INTERFACE` targets. This makes the library turn up like compiled libraries in IDEs such as Visual Studio.
It can also be specified in the `add_library` call but using `target_sources` is more isolated to the CMake version check
Implement constexpr definitions of forward and move to replace usage
of boost::move and boost::forward from the Boost.Move library.
Alter tests to use std::move instead of boost::move.
Remove the dependency on Boost.Move from build.jam