Add a scripting frontend. Documentation and release(7) support coming later.

Scripts take the form:

PARTITIONS=ada0
DISTRIBUTIONS="kernel.txz base.txz ports.txz"

#!/bin/sh
echo "sshd_enable=YES" >> /etc/rc.conf
pkg add puppet

echo "System setup complete"

The second part of the script (beginning with #!) is run in the newly
installed system after the installation onto ada0 (with default partitioning,
see scriptedpart for more complicated scenarios) is complete.