The main library can be found in the "src/modplay" subdirectory. There's a little example player in "src/player.c". To clone modplay and build the example player along with the core modplay library, do the following steps:
git clone ssh://github.com/chn-dev/modplay cd modplay cmake . -B build cmake --build build
After that, you should be able to find the "player" executable in the build directory. If you have any issues using, compiling or porting the library, feel free to contact me.
Have fun and good luck with your projects!
Christian Nowak a.k.a. chn