`git mv src/ opkg-opk/` and update build system
`mkdir common/ && git mv src/defs.h helpers/mode.[ch] common/ && \
	git rm helpers/defs.h` and update build system and sources
Write `common/error.[ch]`:
	`opkg_opk_set_program_name()`, `opkg_opk_error()`, `opkg_opk_errno()`
Ownership override
Finish options handling, remove cli.txt
Reconsider error handling (enum?), prepend program name to messages (see above)
chown and install replacements to append to override file
Test helpers
opkbuild helper to set PATH
ob-buildenv needs to define OPK_WORK_AREA with work area absolute path
Finish documenting functions
Manual page
Handle invalid long options
Clean tests directory
Check OOT
Build with recent GCC, fix warnings
Update POT
Test: build sample package(s) and install with opkg-lede
Search ProteanOS package archive for packages with GNU long names (gcc maybe)?
ob-buildopk should use opkg-opk instead of find/touch/chown/sort/tar/gzip
	Maybe only if opkg-opk is in Build-Depends, to opt into experiment?
opkbuild should depend on opkg-opk, prokit should use if available in root