Prynth 0.52 released - now compatible with the Raspberry Pi 4

Prynth version 0.52 now works with RPi 4 and RPi 3. The RPi 2 is untested but it should also work. The current 0.5x PCBs are still compatible with all of these model B boards.

Downloads are at: https://prynth.github.io/create/downloads.html

As usual, let us know of any bugs, so we can quickly squash them!