Removed library sources, docs, tests and examples; refer to Boost.Config.

This library has been merged into Boost.Config, including sources,
documentation, tests and examples. CI configs are removed as there is
nothing left to test. index.html updated to redirect to Boost.Config.
README.md and meta/libraries.json were updated to mention that the
library was merged into Boost.Config.

CMakeLists.txt and build.jam are retained to define Boost.StaticAssert
targets, which are now empty and only add the dependency on Boost.Config.
This is to avoid breaking downstream libraries that have Boost.StaticAssert
as a dependency. These users will need to be updated, and at that point
this entire git submodule can be deleted.

Author: Lastique