serial_echo.cpp -> example_firmware.cpp
simplify to not buffer input and echo right away
move sources into src/ dir
rename "example_firmware" to "example_firmware.bin" to avoid dirname confusion
make project buildable with the arduino IDE
removed __cxa_pure_virtual work-around

 The declaration of "extern "C" void __cxa_pure_virtual(void)"
 was simply to work-around a linker error which used to happen
 but has evidently been fixed.

 Big thanks to whatever code janitor swept this up!