Optimized the Arduino code to adjust FIRST_PIN and PIN_MAX easily

Hi Sam

I changed your Arduino code a bit. Now it's possible to adjust the first and last pin very easily without changing the whole code. Nevertheless if someone wants a different starting pin than 2 one would have to add a simple offset functionality to the java code, but then it is possible play channel 1 on pins 4,5 or 6,7 and so on. Tried it myself with some adjustments on your master code. If someone wants to use 5.25" instead of 3.5" Floppies an adjustment is very easy too through one single variable. In all these case the code acts fully dynamically. Just if someone wants to combine 3.5" and 5.25" Floppies one would need to adjust some more code, but then the code is not fully dynamically anymore.

What do you think?

Thanks,
Marc