Major processing and error handling overhaul (#8)

* Get rid of initial delay and turn off headers/spaces/etc

* Fix return value/doc for rpm()

* Update ELMduino.h

* Update ELMduino.cpp

* Update ELMduino.cpp

* Update ELMduino.h

* Update ELMduino.cpp

* Update ELMduino.cpp

* Get rid of excess prints

* Update Arduino_software_serial_test.ino

* Update Arduino_hardware_serial_test.ino

* Update ESP32_test.ino

* Update ELMduino.cpp

* Update ELMduino.h

* Update ELMduino.h

* Update ELMduino.cpp

* Update ELMduino.cpp

* Update ELMduino.cpp

* Update ELMduino.cpp

* Update ELMduino.cpp

* Update ELMduino.h

* Bug fixes