* Make the library modular usable.
* Switch to library requirements instead of source. As source puts extra source in install targets.
* Add missing NO_LIB usage requirements.
* 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 doc build to avoid boost-root references.
* Update build deps.
* Rework GHA to use containers for the ubuntu that are god or going away.
* Remove obsolete package installs.
* Need another package?
* Some deepndencies are now C++11 only. Hence date_time is now also C++11 only.
* Switch macOS test to use the latest version.
* Remove not-needed software-properties-common package.
* Remove setup gcc toolchain step.
* Install some missing compilers.
* Maybe the gcc builds for the specific ubuntu versions rea broken. Switch to something newer.
