Listen for the TTY port using udev

To stop the main.c becoming even more unwieldy, most of the code is moved into some new high-level objects, HaegPort and HaegAudio. We also introduce a new object, HaegPortMonitor, to encapsulate the udev interaction.

Closes #1 (closed)

enabled an automatic merge when the pipeline for bf0f91e3 succeeds

canceled the automatic merge

mentioned in commit c2d65c26

merged