Add @gen-built-in and @gen-build-target helpers

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Drop multiple targets

Lets keep it simple

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
docs update

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>