Implement a template format merging subpkg templates into main pkg.

Every generated pkg now must be explicitly defined in a function "<pkgname>_package".
In that function a pkg_install() function is required to explicitly "move"
package files from "main pkg".

The template.options files are now also obsolete (and its do_options() func);
package options should be specified in the package template.

The "subpackages" var is now obsolete. The package list is generated automatically
and sorted alphabetically.