Since this gets used by both the sound backend and the music code it needs to be in a place accessible to both.
# Conflicts:
# src/CMakeLists.txt
# Conflicts:
# libraries/zmusic/decoder/mpg123_decoder.cpp
# libraries/zmusic/decoder/sndfile_decoder.cpp
# src/CMakeLists.txt
The needed headers are now included in the repo, which for these libraries is possible thanks to a stable ABI (at least on Windows, the other platforms still need to be checked but the headers only add, never remove or change existing content.)
The big advantage of this setup is that it allows building the project on Windows without any necessary setup - all that needs to be provided is the DLLs from the binary package.
This still requires some fixes for macOS and Linux. On MacOS the proper library names are missing and the ones for Linux are not verified. Both platforms should work, though, if the dynamic loading is disabled.
