WIP: 16C firmware hack for more memory

[brouhaha]

The first transcendental functions I've tried to add to the 16C are ln, e^x, log (base 10), and 10^x. I have ln actually working, as long as digit entry has been terminated before invoking it. e^x kind of works, but usually gives results 10x what it should be (floating point exponent high by 1), and other times crashes or returns gibberish.

log and 10^x aren't yet working. They're giving the ln and e^x results instead.

Anyhow, I was pretty amazed to be able to compute ln(8) = 2.079441542 on a (hacked) 16C. One small step for a man, one infinitesimally small leap for mankind.

One of the possible issues is that the code uses status register bits 4, 5, 6, 7, and 8, and this may interfere with the 16C's normal use of those status bits. I need to find somewhere to save the status bits before executing the new functions, and restoring them afterward.