version.pl: Add support for daily snapshot releases
version.pl: Add support for daily snapshot releases

Add support for daily snapshot releases of the form
<ordinary version number>-<datecode>.  These are exported to programs
as the new macro __NASM_SNAPSHOT__ (only present in snapshot releases.)

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