* Make the library modular usable.
* Switch to library requirements instead of source. As source puts extra source in install targets.
* Add requires-b2 check to top-level build file.
* Bump B2 require to 5.2
* Update copyright dates.
* Move inter-lib dependencies to a project variable and into the build targets.
* Adjust self dependencies as inter-lib deps no longer apply globally.
* Add Boost.ThrowExceptions transitive dep module.
* Need 22.04 for gcc-11.
* Use latest macOS for GHA.
* windows-2016 is no longer available for GHA.
* ubuntu-18.04 is no longer available for GHA.
* Use ubuntu-24 for gcc on GHA.
* ubuntu-18.04 is no longer available for GHA.
* Use latest clang version on latest ubuntu-24 for GHA.
* Need to instal gcc-9.
* Move include to target.
* Put back disabled CI compilers with hopefully fixed building to account for GHA system changes.
* Fix copy-paste error for cxxstd option.
* Fix to avoid unattended attempt at instal prompt.
* Undo many of the CI changes.
Peter Dimov