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

[bxparks]

I have released v0.10.0 (2024-03-31) of RPN83P here, https://github.com/bxparks/rpn83p/releases. Download the rpn83p.8xk file, then upload it to your calculator. Here are the highlights:

1) The major feature set of this release are the DATE functions:

* date, time, datetime, timezone, and hardware clock
* add or subtract dates, times, datetimes
* convert datetime to different timezones
* convert between datetime and epochseconds
* support alternate Epoch dates (Unix, NTP, GPS, TIOS, Y2K, custom)
* set and retrieve datetime from the hardware clock (84+/84+SE only)
* display time and date objects in RFC 3339 (ISO 8601) format

The hardware clock exists only on the TI-84+ and 84+SE models, not the 83+ or the 83+SE.

The calculator supports the Proleptic Gregorian Calendar from the year 0001 to 9999, using POSIX seconds (no leap seconds), with timezones as fixed offsets from UTC. The Year 2038 problem is avoided by using 40-bit integer arithmetic for all internal date calculations. If none of that made sense, the USER_GUIDE_DATE.md below has explanations and references for those terms.

See https://github.com/bxparks/rpn83p/blob/d...DE_DATE.md
Apologies for its length, 38 pages as a PDF file with almost 500 screenshots.

2) The behavior of CommaEE button has changed from v0.9, because the comma key is needed to enter DATE objects. The EE function now needs to be entered as 2ND EE, as written on the keyboard labels. There is now a MODE option to invert the behavior of the CommaEE button if you prefer.

See https://github.com/bxparks/rpn83p/blob/d...utton-mode

3) The underlying TI-OS supports 27 single-letter storage variables, named A-Z and Theta. I have exposed these through the STO and RCL commands, using the keystrokes `STO ALPHA A` and `2ND RCL ALPHA A`.

See https://github.com/bxparks/rpn83p/blob/d...-variables

4) I improved the speed of the PRIM (prime factor) function by 40-50% with a relatively small tweak. Here are the running times for factoring the worst case number: 65521*65521 = 4_293_001_441:

* TI-83+ (6 MHz): 20 s
* TI-83+SE (15 MHz): 7.7 s
* TI-84+SE (15 MHz): 9.5 s

See https://github.com/bxparks/rpn83p/blob/d...me-factors

5) The RPN83P app now consumes 3 flash pages (48 kiB). So it takes a little longer to upload to the calculator, especially on the 83+ models.

Hope this all makes sense.

Brian