RPN83P: RPN calculator for TI-83+ TI-84+ inspired by HP-42S

[bxparks]

I just released v0.9.0 of RPN83P which contains complex number support similar to the HP-42S, with some features borrowed from the HP-35s. (I have updated the list of features on the original post that I created for this thread.) You can grab the rpn83p.8xk file from the GitHub Releases page. That page also contains a copy of the CHANGELOG for this release.

Please send feedback of the complex number support in RPN83P. As I noted earlier, I can use Free42 as a reference for the HP-42S, but I don't actually have an HP-35s calculator, so I don't know how it handles things which aren't documented in its User's Guide. Also, I have not used complex numbers for, maybe 30 years. I think I recall using them in EE circuit analysis, maybe in E&M, or control theory, or quantum mechanics? I don't really remember. It would be great to have feedback from people who actually use them for real work.

The Complex Numbers section in USER_GUIDE.md adds 12 pages, making it 67 pages long as a PDF file. Sorry about that. A new annunciator for the Complex Display Mode was added to the top of the screen. That forced me to update about 120 screenshots.

If you already know RPN83P, here is my suggestion for getting up to speed on the new features:

* look at the animated GIF in the new Example 4 section in the README.md
* review the Input and Editing section for the new key bindings related to complex numbers
* scan through the new Complex Numbers section
* play around with complex numbers in the app itself, consulting the USER_GUIDE as needed

There is one notable feature that I will highlight here, because I have implemented it differently from any calculator that I am familiar with: In RPN83P, the Trigonometric Mode (DEG, RAD) is completely unrelated to the Complex Display Mode (RECT, PRAD, PDEG). The Trigonometric Mode affects how trig functions perform their calculations. The Complex Display Mode affects how complex numbers are rendered on the screen. The 2 concepts are completely decoupled in RPN83P. It makes sense to me, but I don't know about other people. Complex numbers are always stored internally in rectangular form. The Complex Display Mode controls only the rendering of the complex numbers on the screen.