Documented %xdefine and %xidefine, and fixed an index item in %define.
Documented %xdefine and %xidefine, and fixed an index item in %define.

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