Fix ESPDuino errors

Error-free programming of an ESPDuino.

When programming an ESPDuino I got a java.lang.nullpointerexception in the Arduino IDE. Solution was that I had to explicitly set the "Upload tool" option to "Serial". These are the settings for the ESPDuino:



The upload then proceeds as follows:

-Press both the reset button and the button labeled "Flash" and keep both buttons pressed.

-Click "Upload" in the IDE and wait for it to finish compiling and start uploading. First release the reset button (keep the flash button pressed) and then release the flash button.