wip/HP-1973 0.0 NetBSD

I love the HP-45 calculator. It's beautiful on the outside, but I wanted to show people that it's beautiful on the inside, too. So, as a coding and retrocomputing challenge I decided to rewrite an earlier, terminal-based simulator of mine in Python (but with standalone executables), with a GUI. As with all such 'just a few days on this' projects it spiralled out of control, and the result is HP-1973.

It not only runs (included) ROM code from the HP-45, but also the HP-35 and the HP-80. You can select which calculator you wish to use when the application starts, and also have the option to choose between multiple ROM versions for a given calculator (with warnings if a ROM is known to contain bugs). In total, six calculator-ROM variations are included.