Add macro YAC_VERSION_GREATER_EQUAL

Adding a new header is maybe a bit too much. But I followed this approach, since I wanted to use the macro in a Fortran code and simply #include "yac_version.h". I first tried adding the Macro in yac.h but this did not work. Adding to yac_config.h is also not possible if I understand correctly (and I also think yac_config.h is a somewhat odd name for providing version information).

Todo

• Add tests/mci/test_version.F90 to demonstrate usage.
• Needed in include_HEADERS?