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

[sunpazed]

This a great tool given that any good HP RPN is hundreds of dollars.

I tested your app with an emulator, and it’s really quite good, well done!
It motivated me to purchase a second-hand TI-83+ with Arduino converter cable for $30. I look forward to checking it out on a real device.