add developer section
Force inclusion of a header file for all checked/parsed files. This is an option most static code analyzer support.

- support one ore more header files (comma separated list): sonar.cxx.force_includes=header1.h [,header2.h]
- force include results in #include <...> (system header file)
- files are included in the order of definition (from left to right)
- search path from sonar.cxx.include_directories=...
Merge branch 'feature/force-include' of https://github.com/guwirth/sonar-cxx into feature/force-include