Release v0.1.2

Changed

• moved all feature macros from have_*_.h into new patomic_config.h
• listed new macros in README.md
• updated include paths

Added

• patomic_config.h (with default macro definitions)
• created CompilerFeatureChecks.cmake to check feature macros
• created cmake/in directory for .in files
• added patomic_config.h.in to generate _patomic_config.h
• _patomic_config.h is then included in patomic_config.h

Removed

• all have_*_.h files from src/include/patomic/macros