Updated url, iso filename and md5 for Archlinux x86_64 template
Avoid creating files called "null" in %TEMP% -- Windows has a real NUL device.
Merge pull request #676 from juliandunn/use-windows-nul-device

Avoid creating files called "null" in %TEMP%
Merge pull request #675 from InTheBlue/updateArchLinuxISO

Updated url, iso filename and md5 for Archlinux x86_64 template