add developer section
Merge branch 'master' of https://github.com/guwirth/sonar-cxx
Support variadic macros.
Support GCC's Conditionals with Omitted Operands.

There is a GCC extension which allows the middle operand in a conditional
expression to be omitted. Therefore, the expression "x ? : y" has the value of x
if that is nonzero; otherwise, the value of y.
Support GCC's Conditionals with Omitted Operands #138
Mark the rule change as extension
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