Implement cursor_or_display_shift instruction

[arsdever]

From HD44780U documentation

Cursor or Display Shift

Cursor or display shift shifts the cursor position or display to the right or left without writing or reading
display data (Table 7). This function is used to correct or search the display. In a 2-line display, the cursor
moves to the second line when it passes the 40th digit of the first line. Note that the first and second line
displays will shift at the same time.
When the displayed data is shifted repeatedly each line moves only horizontally. The second line display
does not shift into the first line position.
The address counter (AC) contents will not change if the only action performed is a display shift.

Table 7

S/C	R/L	Details
0	0	Shifts the cursor position to the left. (AC is decremented by one.)
0	1	Shifts the cursor position to the right. (AC is incremented by one.)
1	0	Shifts the entire display to the left. The cursor follows the display shift.
1	1	Shifts the entire display to the right. The cursor follows the display shift.