Expects: AX    0005H
BX    Button to query (0=left, 1=right, 2=center)
                                                                  
Returns: AX    Button status: bit 0 = left button down   (BX & 1) == 1
bit 1 = right button down  (BX & 2) == 2
bit 2 = center button down (BX & 4) == 4
BX    Count of times that button was pressed since last call
CX    X coordinate (horizontal pixel) at last press
DX    Y coordinate (vertical pixel) last press
                                                                  
Info: This obtains:
  The current button status.
  The number of times the specified button (in BX) has been
pressed since the last call to this function.
  The X,Y coordinates of the pointer at the time of the most
recent press of that button.

You might use this to check for double-clicks, or periodically to
check for the press of a particular button (e.g., if the right-
button means to cancel).

Notes: All X,Y coordinates are virtual coordinates and when working with
text mode, you must divide each value by 8 to get a character
clm,row.

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INT 33H 0005H: Query Button-Pressed Counter