* Make the library modular usable.
* Switch to library requirements instead of source. As source puts extra source in install targets.
* Remove relative references to boost-root in Jamfiles.
* Add requires-b2 check to top-level build file.
* Bump B2 require to 5.2
* Change all <source> references to <library>.
* Update copyright dates.
* Move inter-lib dependencies to a project variable and into the build targets.
* Update build deps.
* Replace GHA CI with simpler working one based on alandefreitas/cpp-actions utilities.
* Move project global include to target local include.
* Only msvc gets minor version tests.
* Redo GHA CI to undo move to cpp-actions.
* Remove unavailable libstdc++ package reference.
* Adjust containers and python exe name for current context.
* Remove possibly conflicting dev env setting for xcode.
* Bump some containers for package availability.
* Remove 03 testing as dependencies no longer support it.
* Adjust job names to reflect actualy cxstd tested.
* Tweaks per @pdimov
* also drop failing clang++-libc++
René Ferdinand Rivera Morell