WIP: 16C firmware hack for more memory

[brouhaha]

I just finished testing the new division routine for the register addressing, and it works fine for a moderately large number of test cases. I think now the hacked 16C code handles both program and register memory just fine.

The next thing I'm going to do is change it so that there's no conversion of data memory to program memory as the program grows. There will always be room for 999 program steps, and over 1750 bytes of data memory. This part will likely NOT be compatible with existing Nut simulation on some platforms, such as the ARM-based HP-12C and HP-15C LE, and the SwissMicros Voyager calculators, without hacking the ARM code.

Rather than hack HP's ARM code or SwissMicro's ARM code, I'm planning to write my own. Definitely for the ATSAM4LC2A used in the latest 12C. If that goes well, maybe also for the LPC1115 in the SwissMicros Voyagers.

I've got a few more features I'd like to add to the 16C Nut code. There aren't any vacant key locations, so it will be tricky to come up with ways for the user to access the additional features from the keyboard.