Added direct support for wheel encoders (Arduino Uno)

Added support for wheel encoder counting directly on the main Arduino board.
This allows connecting wheel encoders directly to the Arduino board,
without the need for any additional wheel encoder counter equipment.

For speed, the code is directly addressing the specific Atmega328p ports and interrupts, making this implementation Atmega328p (Arduino Uno) dependent.
It should be easy to adapt for other boards/AVR chips though.