Everyone's a Wally: Routine at E3EC

E3EC: Play square wave sound.

Used by the routine at PlayWaveSequence.
Flip speaker on (set bit 4).
PlaySquareWave	E3EC	LD A,%00010000	A=10 (speaker on = bit 4).
	E3EE	OUT ($FE),A	A=10 (speaker on = bit 4).
	E3F0	PUSH BC	Stash BC on the stack.
PlaySquareWave_Loop	E3F1	DJNZ PlaySquareWave_Loop	Decrease duration by one and loop back to PlaySquareWave_Loop until counter is zero.
	E3F3	POP BC	Restore BC from the stack.
Flip speaker off (unset bit 4).
	E3F4	LD A,%00000000	A=00 (speaker off).
	E3F6	OUT ($FE),A	A=00 (speaker off).
	E3F8	PUSH BC	Stash BC on the stack.
Silence_Loop	E3F9	DJNZ Silence_Loop	Decrease duration by one and loop back to Silence_Loop until counter is zero.
	E3FB	POP BC	Restore BC from the stack.
	E3FC	RET	Return.