modified to update the external flash memory on Einsy boards.
Due to a bug in the USB to serial converter firmware on the Prusa Einsy
boards, the STK500 protocol has been modified to never send semicolon
characters towards the main processor.
This firmware updater is compatible with a modified avrdude using
the "arduino" protocol, see the following commit.
https://github.com/prusa3d/Slic3r/tree/fwupdater_languages
