WIP: 16C firmware hack for more memory

[brouhaha]

I think I've now got a handle on adding float mode operations to the normally integer-only instructions as Garry suggested. I need to do more testing to make sure I haven't broken the integer operations.

I found it interesting that the 16C microcode does such an effective job of making those instructions act as no-ops in float mode that they don't even terminate digit entry or affect the stack lift status.