Find out what happens when paper runs out/printer is disconnected

[fonsp]

https://github.com/klirichek/zj-58 suggests that the TERM signal is sent to the program, but this might only be the case when the filter is run by CUPS.

[fonsp]

The /dev/usb/lp0 device remains, but writing to it blocks execution. Currently needs the Omega to reboot after replacing paper to fix buffer issues (resulting in misaligned images, and probably won't print text properly). I suspect python will throw an exception when the printer is disconnected.
This behaviour is probably fine (since no images are taken from the printi queue when the paper runs out), but the buffer issue should be solved.
This might be fixable with hardware (i.e. turn the omega off when there is no paper).

[fonsp]

Could be fixed by running PrintiClient in a daemon that restarts automatically