0.6.0 - save and restore app state; add carry flag; add BASE ops from HP-16C

• 0.6.0 (2023-09-22)
  • save application state
    • preserve app state into an appvar named RPN83SAV upon exit
    • reconstruct the app state upon restart
  • save X register to TI-OS ANS only on 2ND QUIT or 2ND OFF
    • previously saved to ANS every time X was changed
    • no user-visible change, but is more efficient internally
  • rename P>R to >REC, and R>P to >POL
    • for consistency with other conversion functions, and for consistency
      with HP-42S
    • I prefer the P>R and R>P but the difference is not worth breaking
      consistency
  • support custom MenuGroup handlers
    • absorb changeMenuGroup() functionality into the dispatchMenuNode()
    • add onExit events into changeMenuGroup()
    • add custom mBaseHandler for BASE menu to activate or deactivate
      the baseNumber upon entering or leaving the BASE menu hierarchy
  • BASE mode
    • make all BASE operations use u32 integers, even DEC mode
    • add Carry Flag which is updated for arithmetic, shifting, rotating
      operations
      • add SCF (set carry flag),CCF (clear carry flag), CF? (get
        carry flag)
      • add C or - display indicator
    • remove base number indicator (DEC, HEX, OCT, BIN) from the
      status line (top line)
      • no longer needed since those menu items show a "dot" when selected
      • the base number is only relevant within the BASE menu hierarchy
    • add ASL (arithmetic shift left), RLC (rotate left through carry
      flag), RRC (rotate right through carry flag)
    • add SLn, SRn, RLn, RRn, RLCn, RRCn (shift or rotate Y
      for X times)
    • add CB (clear bit), SB (set bit), B? (get bit)
    • add REVB (reverse bits), CNTB (count bits)
  • add additional HELP pages
    • CFIT Models
    • BASE Ops