rename text files to have .txt extension, etc update references to changed filenames
move out-of-date hints files to the outdated folder. rename the hints files, and hints/include files that are currently named *.2020 to *.370 (next release number).
sys/lib -> sys/libnh sys/lib/libnethackmain.c -> sys/libnh/libnhmain.c libnethack.a -> libnh.a
