added equzero/cmpequ (same as cmpzero/cmpu but only outputs Zero flag)

[ZERICO2005]

__*equzero and __*cmpequ are identical to __*cmpzero and __*cmpu except that they only output to the Zero flag. Currently they just alias __*cmpzero and __*cmpu, but the intent is that they could maybe link to a smaller/faster routine.

__i48cmpzero:
; CC: 13 bytes
; Minimum  :  8F + 3R + 2
; arg == 0 : 11F + 3R + 3
; Maximum  : 14F + 3R + 3
	ex	de, hl
	add	hl, de
	or	a, a
	sbc	hl, de
	ex	de, hl
	ret	nz
	sbc	hl, de
	ret	p
	inc	e
	dec	de
	ret

__i48equzero:
; CC: 10 bytes
; Minimum  :  6F + 3R + 2
; arg == 0 : 11F + 3R + 2
; Maximum  : 11F + 3R + 2
	or	a, a
	sbc	hl, de
	add	hl, de
	ret	nz
	sbc	hl, hl
	adc	hl, de
	ret

Pros:

• No changes to the compiler are needed.
• __*equzero and __*cmpequ give a more clear intent that only the zero flag is needed from the comparison.

Cons:

• The carry flag is unknown when the two arguments are equal for __*cmpequ. Whereas the carry flag will be cleared when the two arguments are equal for __*cmpzero.