HP-41 finally working in Nonpareil

Found the 41CV problem. Released Nonpareil 0.42.

The earlier processor architectures (Classic and Woodstock) set a bit in the general-purpose flag register when a key is set, but the Nut instead has a dedicated flag tested and cleared by its own instructions. My earlier NSIM simulator handled this correctly (mostly), but when I merged the code into Nonpareil, I cut and pasted some code from one of the other processor architectures, and that included setting flag 1. Once I removed that, digit entry and the shift worked fine. The incorrect display character problem I’d noticed before was fixed, although there were still some that were incorrect, most noticably the high-T and lazy-T used to denote alpha string program lines and alpha append. I’d forgotten to include the display C register in the character code.