This routine displays the number of ships passed in the B register followed by a minus sign and the ship icon character passed in the A register at the (y,x) coordinates passed in the X register. If the B-register > 9, then the infinity symbol is displayed.
Note: This routine uses bytes at a negative offset from the stack as temporary storage, so hopefully an IRQ won't happen until the string is finished bring printed!
DP = $D0
A-reg = ship icon character
B-reg = number of ships
X-reg = (y,x) coordinates (Print_Ships only)
X-reg points to (y,x) coordinates (Print_Ships_x only)
D-reg, X-reg, U-reg trashed