We got a lot of the warnings for unchecked Result / tl::expected; let's handle those.
Fix some typos, small errors, debug leftovers. Removed unused mu-cmd-count.cc. Improve test-coverage. Fix manpage. Make the errors for unknown commands a little friendlier.
Esp., better handle the 'no subcommand' case: give the user some more useful help.
Update names, docs etc.
