* Added: the dummy_rpigpio.py module which is a stub for the RPi.GPIO module that is available on the raspberry pi.
* Added: the hd44780.py class which handles the communication with the HD44780 screen through the GPIO ports of the raspberry pi. Note that if there is no available RPi.GPIO module, it uses the dummy_rpigpio module and outputs the screen content to the standard output so that the code can be debugged on a computer
* Added: some error checking and exception handling
* Fixed: percentage formatting to fit the HD44780 screen