Quick customization

Here's a patch set that creates a simple script to do quick and easy customizations of the Autounattend.xml file based on setting 2 or 3 command line switches. For example:

./customize.sh -e 7 -f 'Windows 7 ENTERPRISEN' -p 32
./customize.sh -e 8 -f 'Windows 8.1 PROFESSIONAL'
./customize.sh -e 2012 -f 'Hyper-V Server 2012 R2 SERVERHYPERCORE'

It also helps you by suggesting some full image names if you do not specify one with -f and some editions if you don't specify -e.

In the future, it could be extended to take in an ISO and generate the appropriate config bits.