GitLab

- explicitly added include targets

- fixes bug that we cannot easily change lib versions
- less prone to errors when different versions of libs have different
  dependencies
- consolidated structure of build files

- corrected default list of libdirs to search

- how can we chose between library versions

Feature 9 verify   package behavior when target is already built

See merge request !16

- this ensures always up to date values in substituted files

- to let it run, use the  alias target

- https://clang.llvm.org/docs/JSONCompilationDatabase.html

- older than 2.5 versions still work for comilation but not packaging
- there is no known limitation using scons~=2.5.0