mask! shortening

[jamesbowman]

flashforth/avr/forth/asm.txt

Lines 17 to 18 in 6c56439

	: mask! ( dest1 opcode mask -- instruction )
	rot over invert and rot rot and or ; \ dest1&!mask src&mask or

can be:

>r over xor r> and xor ;

demonstration:

: x rot over invert and rot rot and or ;  ok
: y >r over xor r> and xor ;   ok
aaaa bbbb 0f0f x . ABAB  ok
aaaa bbbb 0f0f y . ABAB  ok