add xor blending mode attempt 2

[Mathman2028]

this version of xor simply cuts out the place where both sprites overlap, instead of bitwise xor'ing the colors in a sense it's xor'ing the alphas

also i actually tested it this time

[balt-dev]

i'm going to work on this tomorrow because i actually would prefer the colors to xor (uou don't have to do anything)