Updating ZXing-C++ to the latest version

[tanius]

Since I just finished updating the ZXing-C++ library dependency for an application where I integrated QZXingNu, I wanted to report my experience to hopefully save you some time doing the same some day.

For updating to nu-book/zxing-cpp commit ed55911 (from 2020-06-19), you would have to:

• In file CMakeLists.txt here, update target_link_libraries(${PROJECT_NAME} … ZXingCore) to target_link_libraries(${PROJECT_NAME} … ZXing::ZXing) (or just ZXing depending on what you decide about Linking to ZXing::Core instead of ZXingCore #4 )

• In file qzingnu.h, update enum class BarcodeFormat (here) with the new values provided in the corresponding class in ZXing-C++. (Maybe you can just rely on that class via #include <ZXing/BarcodeFormat.h> instead of having to copy that code in?)

At that point, builds will work and applications can decode barcodes, but there will be some deprecation warnings in the output. That's because ZXing-C++ has a new interface, demonstrated here for a Qt application and discussed here. I did not yet work that out.