Instead of requiring every Aimee OS project to carry around a full
Portage configuration tree, including patches, saved configurations,
etc., we now support a "layered" configuration system. Aimee OS core
provides a base configuration that includes all settings, patches, etc.
common for all Aimee OS projects. At build time, this base
configuration is combined with the project's configuration, which need
only specify USE flags, etc. for that specific project. This should
make maintenance across multiple projects easier, and make getting a new
project started _significantly_ less cumbersome.
Instead of copying the Portage configuration files to `/etc/portage` and
`/usr/${target}/etc/portage`, the build scripts now use the
configuration directories from the source directory. This avoids issues
with changes (especially removal of files) getting propagated to the
actual configuration paths.