v0.4

In this release the four-color 3.52inch e-ink display has been replaced with a two-color 3.7inch display. This display refreshes much more quicker (~2s) and also supports near-instant partial refresh. The partial refresh is used to superimpose a checkmark (✔) or cross (𐄂) over the QR code when the invoice is paid or timed out.

• The button logic was also changed so that a permanent signal (in this coming from the tray being empty) does not trigger an infinite loop of invoices. However, additional work needs to be done to introduce this behavior for an empty tray at startup, and not just as a tray becomes empty later.
• To avoid an invoice being paid just as the time-out screen is shown, there is a new configurable SUCCESS_SCREEN_EXPIRY, which defaults to five seconds.
• The screen is properly cleaned on shutdown.

The following issues remain in this version:

• While the code has no dependency on RPi.GPIO or Segno, these packages are still installed by the requirements.txt
• the code does not run asyncronously, so while an invoice is displayed the machine does not listen on buttons
• the code doesn't run as a service yet