Refactor global state

[newmanrs]

Having the stack in a module is not the only state that needs access and mutation from the calculator actions, as well as roll-back upon crash.

Create a "State" class that also contains verbose/not verbose modes, toggles for clearing the stack (or not) after commands, and move the stored values into this class as well.

This would also be a good time to store a history of the most recent few actions so that they can be repeated, something akin to rpncalc d4 10 repeat_n to roll 4-sided dice 10 times.

[newmanrs]

e4f4b7e closes