Swap manpage descriptions of HIGH(n) and LOW(n)

[quinnyo]

This corrects the descriptions of the HIGH(n) and LOW(n) functions in rgbasm.5. Each described the other.

Just to be sure, I did compile the following (in)sanity check without issue:

def n equ $ABCD
assert HIGH(n) == (n & $FF00) >> 8
assert LOW(n) == n & $FF

[ISSOtm]

lol nice catch, I wonder how this has been missed for so long :P

I'll merge this immediately, since this is reusing existing markup.

[ISSOtm]

Thank you!