v0.2

In this issue, the machine finally has a display, even though its functionality is limited to showing a simple idle screen at startup. The screen gets cleaned up on shutdown.

• The display is a 3.52inch e-paper display. To accommodate its pins the existing pin scheme had to be overhauled. The display requires eight pins, the outgoing relay occupies eight pins (of which two are unused), and the incoming six buttons occupy seven pins. 23 of the Pi's 40 pins. As the remaining pins are unusable, I doubt the Pi is able to handle a vending machine with eight trays.
• To prepare for the screen, the button and dispenser logic had to be rewritten with the gpiozero package. The RPi.GPIO package is no longer used
• The machine now supports logging. You can configure the loglevel in the .env file
• The machine now has a proper shutdown logic
• Invoices can now also contain the price and currency in their unit
• Fixed some bugs around the configuration options

The improvement wish list remains unchanged.

• Run the application as a service on start
• Verify this code runs on devices other than the Raspberry Pi 2 it was built on
• Eventually this machine should keep listening for buttons even when an invoice is currently displayed. It should cancel the invoice and issue a new one