doc/nasmdoc.src: document additions from preprocessor-rewrite merge
doc/nasmdoc.src: document additions from preprocessor-rewrite merge

letolabs/nasm,turingstudio/nasm,Distrotech/nasm,Distrotech/nasm,turingstudio/nasm,Distrotech/nasm,projedi/nasm,letolabs/nasm,techkey/nasm,projedi/nasm,letolabs/nasm,techkey/nasm,techkey/nasm,techkey/nasm,projedi/nasm,projedi/nasm,turingstudio/nasm,turingstudio/nasm,projedi/nasm,Distrotech/nasm,techkey/nasm