Rewrite febootstrap as a general supermin appliance building tool.

This complete rewrite of the building tools turns febootstrap
into a general purpose, cross-distro, supermin appliance only
build tool.

There is now only one program 'febootstrap' which is used to
build a supermin appliance from a list of packages.

Normal appliances are not supported.

The tools are incompatible with febootstrap 2.x (use the
febootstrap-2.x branch from git to get the old package).