CMakeLists.txt: add RagePhotoB class, improve settings clarification
doc/build.doc: add RAGEPHOTO_C_LIBRARY flag
doc/index.doc: correct RagePhoto.h header
doc/usage.doc: fix minor documentation issue, clarify class differences
ragephoto-gtkviewer: use RagePhotoB class
ragephoto-qtviewer: use RagePhotoB class
RagePhoto-Extract.cpp: use RagePhotoB class
RagePhoto.cpp: LIBRAGEPHOTO_C_API -> LIBRAGEPHOTO_CXX_C
RagePhotoA.hpp: simplify brief
RagePhotoB.hpp: add best implementation detection
RagePhotoLibrary.h: fix WASM C API inclusion by default
README.md: add RAGEPHOTO_C_LIBRARY flag