Maybe:

- If anyone ever finds another adaptor that has the Enter and Shift
  key issues, with a different USB vendor and product ID, add another
  udev rule for it.

- Actual realtime scheduling (maybe). sched(7). Not sure it's
  needed (nice -20 seems OK even while compiling mame with -j5), and it
  might interfere with stuff like JACK. Plus, it would bloat the
  daemon (have to link with -lrt).

- Use a log file instead of stderr, so we can have error/warning messages
  after detaching from the tty. Probably not going to need this,
  users can use -vf for troubleshooting.

- Options to set the virtual device name and vendor/product IDs. Would
  anyone ever need this? KISS principle says wait & see.

- Config file? Do we need it? The udev rules file lets the user add
  options as needed.