compat: ensure proper apkg compat level

apkg status now includes project compat level info and it redirects to new apkg compat command when apkg.compat isn't set to current.

If project compat level isn't set properly apkg compat provides human-friendly instructions on howto update it including upgrade notes when needed.

apkg compat returns exit code 1 when project compat level isn't set correctly so it can be used to ensure compat in scripts/CI too.

Fixes: #61 (closed)