Additional formula logic: NOR, NAND, XOR and XNOR

spauliszyn

Please add the other common formula logic: NOR, NAND, XOR and NXOR

All these can be expressed with a combination of IF's, NOT's, AND's and OR's, but the formula gets long and difficult to follow—it's not as clean. And don't get me started on when you have long phrases as column headers to use as variables!

Right now I can really use an XOR and NXOR, but even a NOT(XOR(a,b)) would be cleaner